Covid Test Paid Cash - Now handed over

My family and I went for Covid Testing on 20/06/2020 in Highway Gardens. Paid for 4 tests by credit card. I have been harassed for almost a year now from Sustainable Collection Services(PTY)Ltd that I owe them money. What a joke. Have emailed receipts etc...still being harassed. To date nothing rectified, still being harassed and they have now loaded collection costs on top of the money that I DON'T OWE THEM.