RCS demand payment after 3 years of account closed

My wife made her final payment for RCS at a Pick and Pay in Cash as there was no eft facilities available at that time. This is about 3 years ago. Knowing this was her final amount due she destroyed her card and threw it away. Her app said amount due is 0.00 and she then requested to close the account. Now after 3 years they came back stating she needs to pay them over R3000.00. The problem is she has already thrown away the Proof of payment slip from PnP. Now the account has been handed over to a Law Firm a now they demand payment. How can they not have received the last payment as the previous ones were made the same way. They are now stating that she must just pay this.. How is this fair????? Why must she pay again? Also this is now affecting her credit rating while she wants to buy a new car... RCS how can the payment not reflect on your side but the app states she does not owe you a cent? What is going on with your systems where nothing matches up... This is really pathetic but as I can see from all the other complaints this is the norm of your business. Please reply to this message so that i can put you in touch with my wife so that this issue can get resolved ASAP