Credit card closure nightmare

I phoned Discovery Bank in February to close my credit card. I was sent an email on how to close it online and a request was put in to convert my miles to rands against the closure. I followed the instructions for online closure on 8 March 2022 and was sent a settlement letter for a balance to be paid by 11 March 2022. At this stage my miles had correctly been changed to rands and were shown correctly on the settlement balance. The settlement letter also stated that my card would be locked. I settled the balance as per the letter on 8 March 2022, deleted the app ( which I had never been able to get onto anyway as Discovery Bank kept trying to upgrade me to another credit card) and took the account to be closed as I had followed everything to the T and within the correct time frame as per the settlement letter. I was sent a statement in April where the miles were changed back to miles, the settlement amount I paid on 8 March was correctly reflected so they had received it timeously, the account hadn't been closed, I was charged for another month's fees, charges other fees I have no idea what they are and charged interest!! I phoned Discovery Bank on 8 April and have been going backwards and forwards with them via phone, emails, through Messenger etc and getting nowhere! They have sent me another settlement letter which I refuse to pay because they should have closed my account on 8 March and the settlement I now have to pay is the extra fees and interest because they didn't close the account when they should have - ie it's their mistake. I refuse to pay this because I had settled and closed the account, the amount of the new settlement makes no sense and I refuse to also continue indefinitely paying settlement amounts and have them not close the account. I don't live in South Africa anymore and just wanted to do the right thing by closing my account properly but their incompetence and the fact that I am going around in square circles has caused me so much stress and trauma. I keep getting messages from them saying they are looking into it and then they start back at square 1 saying I owe them settlement plus they have said they are not locking my card, so my card is open to internet *****. Discovery Bank are ****** and have de*****ed me! I can no longer deal with the mental strain they are causing and would just like them to reverse all the charges for their mistakes and close my account as it should have been done on 8 March 2022. Dealing with them is an absolute nightmare!