Continous Billing

I am on debt mediation and the people that are handling this process gave me a letter to take to bank requesting that they freeze my account. It was delivered at Centurion Mall branch and stamped. But the account has not been frozen and l am being charged bank fees. The letter is a legal document informing you l won't be liable for charges but you have ignored it. My debt was 3500 but it has balloned to 6000 due to bank charges which should not have been charged.