Phone picked up dial up noises?

So I was in California not to long ago visiting family and I went to call my gf, she was still home. The call never even rang which I didn’t find strange since it’s happened to me a lot more than once. So I then tried a FaceTime voice call which went through for about 2 minutes. It’s started cutting out and then I heard other voices that wasn’t my gf, deep voiced cutting through and then what sounded like dial up tones and static and then a loud digital screech like a dial tone that got stuck on a high note and it was so loud it hurt my ears. It then all cut out and then my gf cut back in and was in shock at what I just heard. It’s scared the shit out of me. Any idea what it could have been?