AVPlayer keeps adding streams instead of replacing

I am triggering a video play from a URL. It's just a button, opening the AVPlayerController full screen. If people close it, the can go back to the another item, with possibly a video. There they can click that video to start, however, when they do so, I can hear the audio of the previous player, of the other VC playing in the together with this one. This keeps layering up. How can I avoid this?

This is my class for the videoplayer

import UIKit
import AVFoundation
import AVKit

class simpleVideoPlayer: UIViewController {

var playerController = AVPlayerViewController()
var player:AVPlayer?
var inputVideoUrl: String? = nil

func setupVideo() {

    self.player = AVPlayer()
    self.playerController.player = self.player

}

func playNext(url: URL) {

    let playerItem = AVPlayerItem.init(url: url)
    self.playerController.player?.replaceCurrentItem(with: playerItem)
    self.playerController.player?.play()
}

func setupVideoUrl(url: String) {
    inputVideoUrl = url
}

}

This is in my viewcontroller. It's first getting a URL of a possible advert from my server, if that failed, then it wil just load the "default" video.

let SimpleVideo = simpleVideoPlayer()

@objc func handleTap(gestureRecognizer: UIGestureRecognizer)
{

    ApiVideoAdvertService.sharedInstance.fetchVideoAdvert { (completion: VideoAdvert) in

        let advertUrl = URL(string: completion.video_adverts_url)
        var url = URL(string: (self.article?.video_link?.files[0].link_secure)!)
        var showAdvert: Bool = false

        if (advertUrl != nil && UIApplication.shared.canOpenURL(advertUrl!)) {
            url = advertUrl
            showAdvert = true
        }


        let appDelegate = UIApplication.shared.delegate as! AppDelegate

        if (showAdvert) {
            NotificationCenter.default.addObserver(self, selector: #selector(self.finishVideo),
                                                       name: NSNotification.Name.AVPlayerItemDidPlayToEndTime, object: self.SimpleVideo.playerController.player?.currentItem)
        }


        appDelegate.window?.rootViewController?.present(self.SimpleVideo.playerController, animated: true, completion: {
            self.SimpleVideo.setupVideo()

            if (showAdvert) {
                self.SimpleVideo.playerController.setValue(true, forKey: "requiresLinearPlayback")
            }

            self.SimpleVideo.playNext(url: url!)
        })

    }

@objc func finishVideo() {

    let url = URL(string: (article?.video_link?.files[0].link_secure)!)
    SimpleVideo.playerController.setValue(false, forKey: "requiresLinearPlayback")
    SimpleVideo.playNext(url: url!)
}