Handed over but account paid in full

In March of last year i paid my edgars account up in full, that very same time i called the customer centre from the edgars store in tokai to have the account closed. Unfortunately the system was offline. I then went back 2 days later, and i closed the account. Couple of months later, i recieve a bill of a R170, 80c. I then went back into the store and phoned customer care. I got a email address to the finance department in joburg which i mailed. I have sent numerous faxes, emails. But they are still hassling me and i refuse to pay for something that had to be closed. I have spoken to mohammed who works at edcon and he said he will sort it out. But clearly didnt. They handed me over to debt collectors. And they cannot tell me where, why and how i owe this money if the account is closed.