How difficult is it to remove a phone number?

After posting the same problem on HP & mailing Rozanne directly, I yet again have to contact TFG because they have been unable to remove on old cell number from their computer system! What is so difficult that you can't get it right? Don't you know your own computer system? Each time I've been re-assured that the old number has been removed but only to find out in the following month that the details have NOT been removed. As mentioned before, you are compromising my account security & I want an explanation why this is happening. Are your staff *********** that they can't get something as basic as this sorted out?