***** on my account again after raising a ***** alert.

Please explain to me how I owe you money when my contracts ended and I was on prepaid. First, someone bought a phone on my account. I had to tell you about it. Then you put a ***** alert and somehow you have started deducting 500 from my account. And have been doing so for a while. Please note that the last device I got from you was over 5 years ago. At this point I am convinced that its an inside job and you have no way to safeguard against this because how can it happen twice especially after you put a ***** alert on my contract??? Kindly review this case and complete cancel my contracts because there is no way.