ADT security handed me over to debt collectors

hello peter! I've been handed over to debt collectors for the outstanding amount which I was never told about when cancelling my account with them and now a year later I've been handed to debt collectors. The amount of R350.00 which according to them is still outstanding on my account needs to be payed. I was never told about this when I called to cancel the contract. the contract expired and I told them as soon as the contract expires I need it cancel because I was not leaving in that house anymore. I can pay the amount but my problem is that why wasn't communicated to me. the Sithembiso who did the cancelation even sent me a wrong confirmation cancelation of contract to my email address, with the wrong details to me. it was some else details who also was cancelling the contract but his details where sent to me and just relised that when I opened it after the debt collectors called me. ive been handed over to Debt source and this people call day and night. please help.