Hello there, adi.

It sounds like when you play music, the repeat setting is turned on for what you play. The following link to the online iPhone User Guide provides the instruction on how to change the repeat setting:

Play music - iPhone

Play music

• Control playback. Tap a song to play it and show the Miniplayer. Tap the Miniplayer to show the Now Playing screen, where you can do the following:

   
   
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    Tap to skip to the next song.

     
   
   
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    Tap to return to the song’s beginning.

     
   
   
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    Double-tap to play an album or playlist’s previous song.

     

• Skip to any point in a song. Drag the playhead. Decrease the scrubbing speed by sliding your finger down the screen.

• Share music. Tap , then choose a sharing option.

• Shuffle. Tap to play your songs in random order.

• Repeat. Tap to repeat an album or playlist. Double-tap to repeat a single song.

If you find the issue persists, although this article was written for third-party apps you install on your iOS device, the first set of steps are useful for troubleshooting the Music app, in this case:

If an app you installed unexpectedly quits, stops responding, or won’t open - Apple Support

Restart the app

Close the app and open it again.

Restart your device

Turn your device off and back on.

Check for iOS and app updates

1. Make sure that you're using latest version of iOS.
2. Open the App Store and tap Updates.
3. If updates are available, tap Update All.
4. If asked, enter your Apple ID password. 

You might need a Wi-Fi connection to update some apps.

Thanks for being a part of Apple Support Communities.

Kind Regards.

Hello again, adi.

Thanks for the clarification on the issue you're experiencing. Due to the nature of your issue you may find more information by using another one of Apple's support resources - https://getsupport.apple.com/GetproductgroupList.action to get a more hands-on response.

Cheers.