@Rensza: Which phone to you have? Are you minimising the call screen when you access your voicemail? If so, try tapping the Recent Apps button to see if you can reopen it, then tap the red Phone symbol to end the call. Alternatively, swipe from the top of the screen to the bottom, then tap the red phone symbol in the notification panel. You also have the option of heading to the Phone app > Tap the 3 dots in the top right > Settings > Answering and Ending Calls > Press Side Key To End Calls, and activate this feature. I hope this helps.
