It's quite reasonable to ask for communications to be in writing. That way both sides should have an accurate record of the discussions although it would be worth stating your reason for the request in the correspondence.
The courts do not see anything wrong with bank charges as long as the charges are reasonable (a figure of 8% per year is something than many see as reasonable). I'm guessing that the charges came about because your husband went a few pounds overdrawn and then the bank added a £50 charge and, because that wasn't paid back straight away, they added another £50 and so on until there was little chance of quickly getting the account back on track.
It's possible to make a claim online
Or some people prefer to print the form off and send it to the other party just to provide a last chance to settle before the claim form is sent to the court.
It would be worth contacting the ombudsman to see if they will do anything before taking court action.