If I call one of my contacts,the phone rings to another contact also,why is this?

[AC Question]

While ago I rang one of my contacts, and, after we finished conversation my daughter-in -law rings me to ask what is going on as she answers phone she can hear me speaking language other than english,she realises that I wasn't talking to her and that it means my phone was ringing to her as well.Another time I was calling to my son,and after we finish conversation,my next door neighbour rings me to ask why did I ring her and I didn't ring her at all. Does anyone else have this problem?