For a very long time I've had a Co-operative Bank Visa card which has been paid off for years by direct debit from a bank account. Recently I asked the Co-operative Bank people to change the direct debit to a different bank.
I was first surprised that it took them several months to perform this simple operation, for which I had to fill in a form that they sent me by snail mail (in the 21st century!).
I then discovered after the event (they didn't warn me) that during the operation they first delete the old bank details, then weeks later they add the new bank details, so in the interim they have no bank details on file, and the card doesn't get paid off. This they regard as my fault. "You could have sent a manual payment." Well, yes, I could, if I'd had any reason to think it was necessary.
The whole thing is so incredibly slow and incompetent. They've got the old bank details and the new bank details, why should it take them more than a minute or two to replace the former with the latter? And, even if they insist on moving in slow motion, why remove the old bank details before they're ready to put in the new bank details?