The two look similar enough that unless the web photo were sitting right next to it, the cutter at the shop probably wouldn't have noted a difference in the first instance. That being said, it is not the same fabric, it is their mistake and they should rectify it including return postage. If it came via UPS or FedEx, the shop can sent you a prepaid return label that you can drop off at any local site. If you paid by credit card or paypal file a complaint. I would also suggest that you print a screen shot of the fabric from their website to support your position. Alternatively the shop invoice may have the manufacturer's code which should be different from the one on your initial web receipt.
It's entirely possible that they never had the fabric you were seeking and only grabbing fabric swatches off the manufacturer's site to put up on the internet rather than scanning their own. However, if the shop is interested in retaining customers they should satisfy and mentioning the fact that you are on lots of lists where things like this are discussed may have some impact on an ebusiness.