handing over an account i wasn't even informed abt

I had two contracts with cell c one taken in 2011 and another one in 2012. when the one from 2011 ended in Jan 2013, they continued airtime and billing me, I called them to stop as I had no desire to extend or renew it. the call centre told me to go cancel it at the shop where I took it, which did not make sense cause wen I signed a contract I signed that it should be stopped at that particular date. other contract was due to end the following year, at some point they debited 3 times the amount they should have, I queried that up till today no one got back to me as to why that happened. they continued with the debit orders until I don't know when it stopped. I stopped hearing from them then, then today I receive an email that I need to settle an account of almost R4000 in the next 4days, I don't understand how cell c failed to contact me as they have always did, my alternative number, email and physical addresses are still the same. why was I not contacted if my account went to arrears cause when debit orders stopped and they didn't say anything I was relieved that i'm done with them, but for them to only contact me 2years later. I need some serious clarification