If this happened to me I would try everything possible to stop the payment. If I wrote a check or used a debit card - I would pay the stop payment fee at the bank. If using a credit card - I would be calling the cc company to see if the purchase was large enough to be covered by the guarantee policy. I would certainly report this store to the Better Business Bureau.
I agree with you - it sounds like they are making mistakes on purpose. I am sick of feeling like I've been robbed everytime I go shopping or open the mail. I have started fighting back and I don't care who I make mad. Good luck with this - I hope the shop owner makes things right for you and apologizes for the rude, poorly trained employee he/she has hired and trusts with their customers and business.