Unacceptible accounts behaviour

A number of years ago we cancelled our account with Chubb Security in full accordance with their terms & conditions. Over the last three and a half years we have repeatedly received statements claiming that we still owe them fees. I have repeatedly communicated with Chubb accounts department only to have them agree that this was a mistake on their part. We have now received a final letter of demand claiming over R 10,000 for unpaid fees as well as threatening to submit my Mother (In whose name the account was in) with legal action as well as submitting her name to various credit bureaus). This has to be the most disgusting behaviour from any organisation that I have dealt with. Chubb, get you facts straight before threatening people. Christian Giesen ***