BT Phone Problem

I got in touch with Ofcom who gave me a case number and a special BT number to complain to. This expedited the whole thing. The problem is now sorted, I have been refunded. I have not got a satisfactory answer as to how I was billed for someone else's phone, or rather how their phone was linked to my address other than to say it was a crossed line. The other person clearly knew as they were not getting bills and when I called and left a message, twice, no return call and a sudden increase in calls from the number.

Anyway, the main thing, I got a refund, the number has been cut off, and I am only paying the bill for my own phone now.