It is difficult to tell what you are asking. Here is a possible rewrite. Dear sir I am writing concerning customer service at you bank. On weekdays, the bank's clients are allowed to schedule multiple appointments with the staff. This is causing slower service because of the overbooking of your staff. Customer service would be improved if this overbooking was decreased. I look forward to hearing from you Yours faithfully

Thia is tricky since i am not sure what you are trying to say. one thing that is clear though is you are not writing about the bank staff but instead are concerned about the process or consequences of the processes that they have in place.