Bridal Shop of Horrors

I have had a tug of war with a bridal shop regarding my wedding dress. I live on the west coast and bought the dress near my family in the mis west. The dress came in two weeks ago. For various reasons that
would take too long to explain, the shop was not going to get the dress shipped to me in time for it to be altered. After paying for shipping and for a pair of shoes, they are both in with my father and will be shipped by him-on time. The problem is, when the dress was picked up today they told my sister
i had to pay sales tax on the dress. They used the shipping charges as credit and she paid the rest.
When I bought the dress the price was written in a contract that had sales tax waived with a line through that space. They charged me aboved and beyond what was agreed in the contract. At the time I bought the dress they told me they would roll the sales tax into the price we agreed and signed on. They did as a courtesy because I live in a state that has no sales tax. These people have treated me horribly and now have sqeezed more money out by this sales tax thing. The dress was paid in full and my sister paid the sales tax bit because she didn't want to argue with them anymore. I feel they could not legally charge me for sales tax after the contract price was signed andaiad in full. What do I do?

Based on what you say here, you could file suit against them (or at least threaten to do so) in small claims court or in regular court; filing in small claims court is easier and requires no attorney...