I think that the answer given by ummm was correct in the reasons why the bank does not allow anyone to use a personal account as a business account. The same goes for a personal credit card, I remember being warned by our credit card company when we put more than usual amount of transactions on it, that it must not be used for business transactions.
I guess that there will be something in the t&c's that says a personal account cannot be used as a business account. It does stand to reason to do this or we could all avoid bank business charges by using personal accounts. I would double check this before you send a letter accusing your bank of slander, they could advise you that they will close your personal account, as you have not complied with the terms and conditions and you may be left with egg on your face!
And yes, banks do charge for banking cash, although I believe that some banks will let some businesses have elements of banking free, if their turnover is under a certain amount each year.
Hope this helps
Sue