Of course it's a charge. That's how products and services work - the bank supplies it and charges you a fee to carry out that service. If your bank was sensible they will have written to you telling you that they were going to take interest. My bank write to me every month telling me how much my overdraft is going to cost, and exactly when they're going to take it out. Again, if you think a service is too expensive, then why are you using it? The terms and conditions for my account use the terminology "service charge", which is exactly the same as "charging for a service".