Harbor Freight Tools Overcharged my credit card for Tax on a discontinued item and refused to refund money. Internet

I ordered 2 tools over the harbor freight web site. One of the tools were discontinued and not in stock. They sent me the other tool I ordered but still charged me sales tax and shipping on the Tool that was not sent and discontinued from stock. When I called Customer service to get a refund on the shipping and sales tax. they gave me a refund on the shipping portion but not on the sales Tax they charged me on the item that was cancelled from my order. After 4 calls and 4 arguments their customer service rep,s refuse to acknowledge that they owe me any more money. It is so frustrating to talk to these pepole that don't have the apptitude to figure out simple math. It isn't a large amount of money but it's the principle of the matter. If you must shop at Harbor Freight to buy their cheap low quality tool's don't do it over the internet because if something goes wrong you will be up the creek without a paddle.