Last year, bmibaby did the same thing to me. I paid with a debit card to avoid the cc fee. They charged the £3 anyway.
I called them up to get it refunded and they initially said they didn't do refunds in any circumstances unless I put the request in writing. An argument ensued after which they eventually agreed to refund the £3. They never did though.
Avoid these people. They are con-artists.
Martin.