Random joined my private FaceTime call

‘AttachedDemerity’ joined my private Facetime call with my friend. It wasn’t one with a link, just a regular call. I didn’t track the number, they just didn’t say anything and then left. We both kept being kicked out of the call, and my friend was kicked out when it happened. They then joined and was extremely confused. My friend is NOT just doing a prank, and we are both kinda scared.