My bullet in my pygame game won't delete and just pass through the enemy

I am creating a simple game where you would shoot an enemy/ufo. Whenever I shoot the enemy it would pop/disappear, however the bullet won't (Python didn't give me any traceback error). Also when I tried to use the colliderect, nothing seems happening but when I used the collidepoint, it worked.

By the way, here is the full code:

import pygame, sys, random
from pygame.locals import *
from pygame import mixer

pygame.init()

WINDOWWIDTH  = 800 # Width of the screen
WINDOWHEIGHT = 550 # Height of the screen
FPS          = 20
WHITE        = (255, 255, 255)


class Player(pygame.sprite.Sprite):
    """
    This is the class for the player and the other functions for the program.
    """
    def __init__(self, DISPLAYSURF):
        pygame.sprite.Sprite.__init__(self)
        self.PLAYER      = pygame.image.load('SpaceRocket.png').convert_alpha() #SpaceShip by dawnydawny from Pixabay
        self.XPLAYER     = WINDOWWIDTH / 2
        self.YPLAYER     = WINDOWHEIGHT - 75
        self.FONT        = pygame.font.Font('freesansbold.ttf', 15)
        self.PBOX        = self.PLAYER.get_rect()
        self.PBOX.center = (self.XPLAYER, self.YPLAYER)
        self.DISPLAYSURF = DISPLAYSURF
        self.color       = WHITE
    
    def makePLAYER(self):
        self.DISPLAYSURF.blit(self.PLAYER, self.PBOX)
    
    def spaceMessage(self, message):
        self.message = message
        self.mesg    = self.FONT.render(self.message, True, self.color)
        self.MBOX    = self.mesg.get_rect()
        self.MBOX.x  = (50)
        self.MBOX.y  = (WINDOWHEIGHT - 500)
        self.DISPLAYSURF.blit(self.mesg, self.MBOX )
    
    def showScore(self, score):
        self.score = score
        self.spaceMessage("SCORE: %s" % score)
    
    def terminate(self):
        pygame.quit()
        sys.exit()
    
    
class UFO(pygame.sprite.Sprite):
    """
    This is the class for the UFO.
    """
    def __init__(self, XUFO, YUFO):
        pygame.sprite.Sprite.__init__(self)
        self.XUFO        = XUFO
        self.YUFO        = WINDOWHEIGHT - 570
        self.UFO         = pygame.image.load('SpaceUFO.png').convert_alpha() #Image by Mostafa Elturkey from Pixabay
        self.UBOX        = self.UFO.get_rect()
        self.UBOX.center = (self.XUFO, self.YUFO)
    
    def makeUFO(self, DISPLAYSURF):
        self.DISPLAYSURF = DISPLAYSURF
        self.DISPLAYSURF.blit(self.UFO, [self.XUFO, self.YUFO])
    
    
class Bullet(pygame.sprite.Sprite):
    """
    This is the class for bullets.
    """
    def __init__(self, bulletx, bullety):
        pygame.sprite.Sprite.__init__(self)
        self.bulletx        = bulletx
        self.bullety        = bullety
        self.SpaceBulletIMG = pygame.image.load("SpaceBulletIMG.png").convert_alpha() #Image by Clker-Free-Vector-Images from Pixabay
        self.BBOX           = self.SpaceBulletIMG.get_rect()
        self.BBOX.center    = (self.bulletx, self.bullety)
    
    def makeBullet(self, DISPLAYSURF):
        self.DISPLAYSURF = DISPLAYSURF
        self.DISPLAYSURF.blit(self.SpaceBulletIMG, self.BBOX)
    
SpaceUFO    = []
SpaceBullet = []
def runGame(Player):
    global FPSCLOCK, BACKGROUNDIMG, DISPLAYSURF, SpaceUFO

    DISPLAYSURF   = pygame.display.set_mode((WINDOWWIDTH, WINDOWHEIGHT))
    BACKGROUNDIMG = pygame.image.load('SpaceBackground.jpg') # Image by Free-Photos from Pixabay 
    FPSCLOCK      = pygame.time.Clock()
    Player        = Player(DISPLAYSURF)
    SpaceKill     = 0
    SCORE         = 0
    BulletSound   = mixer.Sound('BulletSound.wav') # From https://www.freesoundeffects.com/
    pygame.display.set_caption('Space Fight by MadCoderErrr')
    mixer.music.load('SpaceSound.mp3') # Music: https://www.bensound.com
    mixer.music.play(-1)

    if SpaceKill > 0:
        SpaceKill += 1
    if SpaceKill > 10:
        SpaceKill = 0

    while True:
        DISPLAYSURF.blit(BACKGROUNDIMG, [0, 0])
    
        for event in pygame.event.get():
            if event.type == QUIT:
                Player.terminate()
            
        if len(SpaceUFO) < 5:
            SpaceUFO.append(UFO(round(random.randrange(0, WINDOWWIDTH - 20.0 ** 2) * 20.0) / 20.0, WINDOWHEIGHT - 570))
            print('making new aliens')
            continue
        
        for ufo in SpaceUFO.copy():
            ufo.makeUFO(DISPLAYSURF)
            ufo.YUFO += FPS / 4
            continue
        
        for ufo in SpaceUFO:
            if ufo.YUFO >= WINDOWHEIGHT:
                SpaceUFO.pop(SpaceUFO.index(ufo))
                print('Alien is gone')
            
        for bullet in SpaceBullet.copy():
            DISPLAYSURF.blit(bullet.SpaceBulletIMG, [bullet.bulletx, bullet.bullety])
            if bullet.bullety > 0:
                bullet.bullety -= FPS
            if bullet.bullety < 0:
                SpaceBullet.pop()
                print('Bullet is now gone!')
            continue
            
        if SpaceBullet:
            for bullet in SpaceBullet.copy():
                for ufo in SpaceUFO.copy():
                    if ufo.UBOX.colliderect(bullet.BBOX):
                        SpaceBullet.pop(SpaceBullet.index(bullet))
                        SpaceUFO.pop(SpaceUFO.index(ufo))
                        print('hit')
                        SCORE += 1
                        break
    

        if SpaceBullet:
            for bullet in SpaceBullet.copy():
                for ufo in SpaceUFO.copy():
                    if ufo.UBOX.collidepoint(bullet.bulletx, bullet.bullety):
                        SpaceBullet.pop(SpaceBullet.index(bullet))
                        SpaceUFO.pop(SpaceUFO.index(ufo))
                        print('hit')
                        SCORE += 1
                        break
                    if ufo.UBOX.collidepoint(bullet.bulletx - 10, bullet.bullety):
                        SpaceBullet.pop(SpaceBullet.index(bullet))
                        SpaceUFO.pop(SpaceUFO.index(ufo))
                        print('hit')
                        SCORE += 1
                        break
                    
        if event.type == KEYDOWN:
            if event.key == K_LEFT and not Player.XPLAYER <= 0:
                Player.XPLAYER -= FPS
            if event.key == K_RIGHT and Player.XPLAYER < WINDOWWIDTH - (FPS * 3):
                Player.XPLAYER += FPS
            if event.key == K_SPACE and SpaceKill < 10:
                if len(SpaceBullet) < 10:
                    SpaceBullet.append(Bullet(Player.XPLAYER, Player.YPLAYER))
                SpaceKill = 1
                BulletSound.play()
            
        Player.showScore(SCORE)
        DISPLAYSURF.blit(Player.PLAYER, [Player.XPLAYER, Player.YPLAYER])
        FPSCLOCK.tick(FPS)
        pygame.display.flip()
        pygame.display.update()
    
    if __name__ == '__main__':
    runGame(Player)