I did and she is totally shocked by there attitude and has told me if you wish to persue a legal case she would back me.
Is she threatening to end her agreement with the clampers unless they reimburse you? If not get her to speak to the boss of the clamping firm.
The clampers are far more likely to listen to one of their customers (ie that shop) threatening to end their contract with them, than someone who has been clamped. It'll be more cost efficient for them to refund you, than to lose that agreement. Commercial pressure is better than pursuing legal remedies.