Hassle trying to settle credit card

It's amazing how banks are so quick to offer you credit but have to find every possible reason to make it impossible for you to cancel/settle. I'm currently battling to cancel a Nedbank credit card because apparently you get quoted a different amount for doing a cash deposit and EFT transfer. I tried to settle the account via EFT which proved to be a nightmare so i did the logic thing, withdrew the amount quoted and went straight to the branch and paid thinking it will reflect within no time on their side and i will call in the next day to settle, well surprise surprise, i can't settle because they charge interest per every R100 deposited so i must pay a further R290 odd before i can settle, now we all know where this is going...an ongoing cycle of oh there was an extra days charge on interest so it's no longer R290 it's R300+ and, and, and.

Now here is my thinking, yes i called in trying to do an EFT transfer and requested the settlement amount, after struggling i went and paid the money at the branch, how was i as a client supposed to know that the settlement amount would be different based on the method of payment i use, how was i to know that i was supposed to call them back and say "hey guess what i'm struggling to pay via EFT so i'm going to withdraw the money and payment at the branch would you please give me a new settlement amount"? I just wonder how many other people who are not bankers would understand this logic.

To think i have a loan of over R80k and car finance of over R250k with these people, never missed a payment on any of them, and i go through such a hassle to cancel a credit card.