music coming on during phone calls

So I have a 2013 Prius two and a 2018 Prius C - both cars have this issue - when you're on the phone (through the car) and music randomly starts playing over the phone call - the other person can't hear the sound. We only have Iphones so its Itunes that starts playing, I have found it happens more often when I'm playing music off of Pandora or Amazon Music etc and get a call that is long lasting, the music starts randomly playing and not from what was being listened too but from Itunes. Anyone have any suggestions????