Wrongly accused of owing the Store

I had an Edgars account back in 1996. I tear the card because I dint wanted to buy anything again. I went to Edgars Van der Walt Street on the upper level at account payments and told them to cancel the magazine and any other benefits adding to my instalment. they did cancel in my present and I started paying it off. I remember paying it with my id book as I had no card and my last payment was less than 50.00. I asked them to close the account. after than I never heard from Edgars until this year 2017 contacted by other people claiming to be collectors on behalf of Edgars saying I owe the store more than 1000.00. I told them I don't owe the store that and I have cancelled the account long time at the branch and paid up all. I even asked them if I really owed the store why did they kept quite for more than 15 years and only came to me this year 2017, were they waiting for the amount to accumulate or what but they insist that I owe Edgars that amount and that the account was never cancelled and they requested a cancellation letter of which I wont have as I did the cancellation myself by personally going to the store and the cancellation and closing was done in front of me. I tried calling the Edgars store at Van der Walt but they don't answer the phone and this collectors are making my life a living hell.