OK. They tried that one with me too!
I was well over my limit (mainly due to charges).
They wrote to me and said 'You are a naughty boy, you owe us £1300. How are you going to pay it back, return your cards & cheque books etc'
My reply was 'When you give me back the £5000 you took from me,that's when'.
They wrote back and said 'We've already told you to sod off so how are you going to repay it?'
So I went to moneyclaim and filed on their a***s.
That cost them nearly £1000 more in interest btw.
Needless to say I was able to comfortably pay off my overdraft shortly afterwards.