ADT's *********** system

I cancelled my alarm contract with ADT in January 2014. The equipment was subsequently removed. The monthly installment went off via debit order every month. Now all of a sudden, I receive a letter of demand from Debtsource for R377.69 and the ridiculous fee of R3500.00 for Debtsource! Really!!! I have forwarded all the relevant e-mail correspondence addressed to ADT to Debtsource without even as much as an acknowledgement from them. Now they have started sending threatening and offensive sms's. I have never once received any form of communication from ADT informing me about the outstanding amount. I gave notice, the last debit order was collected by ADT and 18 months later threatening letters and sms's. Nice one ADT! Make sure of your facts before you do stupid things like this! S.D. GEBHARDT