Sorry but not in this case..... charges for cash withdrawals and the variable interest rate quoted, are part of the user agreement T & C's that you agreed to when you signed the agreement.
It is your responsibility to ensure the interest and any cash withdrawal fee does not take you over your agreed credit limit in the first place.
However charges that are seen as excessive in relation to the amount over your limit, could be challenged on the grounds of a fine or penalty being imposed. which would be unlawful. This can be demonstrated when a letter that should reasonably cost no more than an example of say £2.50 ....actually ends up with a charge / fine of £30 being applied to your account.