My bank taking the mick?

[Amateurish]

Interested in people's thoughts here. I got a letter from my bank about an account which I thought I no longer used. Apparently I owed about £65 on the account. So I went online and saw that this related to a £20 spend a number of months ago which had then grown with interest and charges etc. OK, my mistake, fair enough. So I went online and cleared the balance. Job done - or so I thought. Fast forward a couple of months and I got another letter saying I still owed £60 odd. Must be some mistake - so I checked again. This time the bank had levied debit interest of a few pence *after* I cleared the balance. Then hit me with several charges again since the account was once again overdrawn. So now back up to £60 odd.

So should I tell them where to go? Or is it my mistake?