Call conversation was intercepted

Hello, I was just on my iPhone with my boyfriend having a conversation. Somehow, his daughter was able to hear our conversation from her iPhone. She was on the call all of a sudden with her dad and myself. At no time did I hear a ringing like you would for a 3way call. How is this possible??

And shortly after we hung up, none of my iPhone buttons would work. My phone froze then apps would light up like someone else was controlling my phone.

This has never happened before.