Calls get rerouted across the globe?

When I call my dad from my cell phone to his cell phone I've gotten lines crossed somehow and end up listening to someone having a one sided conversation in a indiscernible language. It doesn't ring when I press the call button it just goes directly to this other call. I can't hear both sides of the conversation in the other language. The first time was a woman speaking what sounded like an African dialect maybe the second time it happened it sounded like a man speaking hindi perhaps. Is this from him downloading suspicious stuff on his phone? If so, how does he fix it? It doesn't happen every time I call him but it happened twice last week and it's never happened before and I've never heard of this happening before to anyone else.