Chubb security

I sold my house in Jan and I immediately informed Chubb as I had an account with them and requested them to terminate my contract as I no longer use the alarm system till today they havent deactivated my acc and they still deduct money every month.Every time I call they promise to phone me back or they will send an email to the relevant department to deactivate the Acc. I am tired as this is messing my credit record because I reverse debit order every month.please assist