Disgusting service from Discovery that does not even know how its own accounts work

I have only given one start here because it is not possible to go lower. My husband got an Apple Watch on the rewards programme with Discovery. The Discovery credit card was placed on a debit order. In Feb 2020 Discovery made a mistake and did not deduct the correct amount resulting in the account being in arrears. My husband spoke with Discovery and they committed to taking an additional debit order to cover the amount in arrears due to their mistake. Next thing we are harassed by debt collectors saying we owe over R4000 on the credit card! There was not a time ever when this account had such a high amount outstanding, every statement from Feb 2020 until now does not show that amount. When my husband called Discovery they told him that this is not outstanding, the only amount outstanding was still the amount that was not debited in February, which, even after asking for this to be corrected, was not done. So we made a payment on the account that put the account into the positive. We are still being harassed by the debt collector and still when phoning the Discovery accounts we are told that this amount is not outstanding and when phoning Discovery Vitality they say that the account is in arrears and that Discovery cannot help us with the matter we have to deal with the debt collectors!!!!!! The debt collectors state we do owe the money according to Discovery. How is this matter supposed to be resolved? Why was this handed over in the first place?