Flutter: "Could not resolve all artifacts for configuration ':classpath'"

I am trying to run a default flutter app but when I run it gives the below error:

Running Gradle task 'assembleDebug'...

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring root project 'android'.
> Could not resolve all artifacts for configuration ':classpath'.
   > Could not resolve com.android.tools.build:gradle:3.5.3.
     Required by:
         project :
      > Could not resolve com.android.tools.build:gradle:3.5.3.
         > Could not get resource 'https://dl.google.com/dl/android/maven2/com/android/tools/build/gradle/3.5.3/gradle-3.5.3.pom'.
            > Could not GET 'https://dl.google.com/dl/android/maven2/com/android/tools/build/gradle/3.5.3/gradle-3.5.3.pom'.
               > Connect to 172.30.0.15:3128 [/172.30.0.15] failed: Connection timed out: connect
      > Could not resolve com.android.tools.build:gradle:3.5.3.
         > Could not get resource 'https://jcenter.bintray.com/com/android/tools/build/gradle/3.5.3/gradle-3.5.3.pom'.
            > Could not GET 'https://jcenter.bintray.com/com/android/tools/build/gradle/3.5.3/gradle-3.5.3.pom'.
               > Connect to 172.30.0.15:3128 [/172.30.0.15] failed: Connection timed out: connect
   > Could not resolve org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.50.
     Required by:
         project :
      > Could not resolve org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.50.
         > Could not get resource 'https://dl.google.com/dl/android/maven2/org/jetbrains/kotlin/kotlin-gradle-plugin/1.3.50/kotlin-gradle-plugin-1.3.50.pom'.
            > Could not GET 'https://dl.google.com/dl/android/maven2/org/jetbrains/kotlin/kotlin-gradle-plugin/1.3.50/kotlin-gradle-plugin-1.3.50.pom'.
               > Connect to 172.30.0.15:3128 [/172.30.0.15] failed: Connection timed out: connect
      > Could not resolve org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.50.
         > Could not get resource 'https://jcenter.bintray.com/org/jetbrains/kotlin/kotlin-gradle-plugin/1.3.50/kotlin-gradle-plugin-1.3.50.pom'.
            > Could not GET 'https://jcenter.bintray.com/org/jetbrains/kotlin/kotlin-gradle-plugin/1.3.50/kotlin-gradle-plugin-1.3.50.pom'.
               > Connect to 172.30.0.15:3128 [/172.30.0.15] failed: Connection timed out: connect

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 2m 25s
Exception: Gradle task assembleDebug failed with exit code 1

below is the build.gradle code:

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        google()
        jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.3'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

The whole code of the app is default one, no changes have been done I have just connected an emulator and tried to run if it works and am stuuck at this assembleDebug error. If anyone has any idea where Im going wrong please do comment...