I think you need to be a bit careful about accusations of "price fixing". i.e.
"Price fixing is an agreement between business competitors to sell the same product or service at the same price"
Any discounts given are surely up to the sales person in the same way that if you and I both buy a car the price could be discounted differently depending on a number of factors.
I'm a bit unclear....What was the advertised price for the items you bought and is that what you paid? If the price came up more then I would imagine it should be corrected. If they are stating that it is policy to charge more than the advertised price then that probably isn't legal.