Have I been hacked?

Today I received imessages that appeared to be from a friend I was on facetime too at the time. They knew nothing about the messages and denied sending them. They also took a screenshot of their phone which showed messages that they'd sent earlier but not the strange messages I was receiving. We thought it odd but couldn't explain it. Later I got a facetime call which appeared to be from the same friend, but it was a complete stranger demanding to know who I was and why I kept calling them. I apologied but said I had no idea who they were, but they were coming up as one of my contacts. I fear there was something sinister as they didn't show their face in entirity and I could hear a third party in the background whispering. I ended the call and immediately changed my apple ID and advised my friend that they were appearing as to do the same (not by imessage). Have I or my friend been hacked or is there a problem with imessage and facetime?