Another way of dealing with this sort of problem (although jantimot managed well without having to resort to this) is to pay by credit card and then when you get the statement, dispute the transaction. If the circumstances warrant it I would have no compunction even about lying if it were necessary; not that it ever has been. I have never had to pay a disputed credit card transaction, and there have been a few.
At the very least it will need them to investigate and frame a reply. I suspect most of the time it simply isn't worth the effort.
