I'm with Barclays and they took �15 because i told them to cancel a standing order and they didn't so it bounced. They simply refunded me as it was their fault.
I also have a recent fairly large email about your topic but not sure how to get it to you, way too much to put on here! x
today i have had a letter from the halifax giving me back over two thousand pounds that i have been charged over the last six years!!!
my account is still open and it doesnt affect your credit score to my knowledge.
there is another thread on here that has quite a few comments, but on there i posted a few very helpful sites.
You are likely to get your account cancelled if you actually start court proceedings - they will pay up rather than go to court but will cancel your account.
If you are persistent with letter writing and succeed that way they are unlikely to cancel your account.