Frustrated client

Foschini group has handed us over to the attorneys for a payment that we did already in 2015. My husband had an account with Markham while we were still in University around 2006. Unfortunately he couldn't pay up the account because he was a student with no money.so he was owing Markham all these years. In 2015 we app**** for a bond but we were told to pay up Markham because they listed us we can't get the bond until the debt is paid up. The amount due was around R700. We paid up the amount due and we were approved. After we made the payment two years later the lawyers have been calling us none stop saying that we owe Markham. We told them that the payment was made in Markham Golden Acre in Cape Town CBD but unfortunately we lost the receipt since we have been moving around a lot. We were told to go to the store but the store said they couldn't retrieve the payment. It's very sad that Foschini group expect us to pay again. The agents that have been calling us always tells us that they will investigate the matter but they will just keep quiet for few months and then decide to phone us again. I ask them if they don't have notes on their system so that they can do what's needed to be done on their side before they phone us again. It's not nice to be harassed like this by these people. R700 is not a lot of money to pay but it's a lot if you must pay it more than once and it's frustrating.