Hi,
Here are a few comments.
You need to add an introductory paragraph. Tell then your account number and type of account, etc. Explain briefly why and when you were charged this penalty.
I suggest that there is no point in saying it is not 'fair'. Banks don't care about 'fairness'.
I don't think it is wise to tell a bank that something is 'unacceptable'. It will antagonize them, and they can try to force you to pay if they want to. Instead, be nice. Tell them that you are a good customer, and ask for their assistance.
If you wish, revise your letter and post it here again for more comments.
Clive