SNAP!
I was a little older though, I think 7 or 8. The guy used a very long word beginning with ‘m’ (please dont make it spell it out) and I remember telling my dad that a man rang and asked if I would like to listen to him M’ing.
We had to change our number and I had to recall the conversation to a very lovely police woman.
I never picked up the phone after that. In fact, I still don’t.