Bad service at Discovery Bank call center

I have had a Discovery credit card for many years. I acquired it as I am with Discovery Medical Aid. I am also with FNB for more than 50 years. FNB always administered the Discovery credit card. All was well. Now Discovery Bank has taken over the administration. What a disaster. I have had endless problems. They initially did not inform card holders how to pay the account. When they then did it I had to visit FNB twice before that went smoothly. I have had enough. I have spent close onto R100 in phone calls(I am a pensioner and have a prepaid phone) to sort out the various hitches resulting from the banks bad administration. I eventually called to cancel the card. The operator then told me to call in. I said why not lodge it now? She said reluctantly that she would. Of course, nothing has been done and although I have paid the card in full and not used it again I am now sent an account for R488. (Miles fee, R423,card fee and some other fee)I also requested that they phone me. One has that option. That was to have taken 24 hours. Of course it did not happen. I always phone around 5:30 am so that I would have to wait forever for an operator and have awful music playing in my ears. My question is: How on earth do I cancel the credit card?