Cohen's Fashion Optical

I purchase eye glasses (consider health care service) from this store. They scam me by saying they will give me $100 off from their glasses frame in the store. The frame is $399 with $100 off is $299. A day later I found out that glasses frame is normally sell in another store for $49-$59. I went back and ask Cohen's to return but they said they can only give me a store credit plus the staff was very rude with an attitude. They probably use this trick to so many consumers. I want to get a refund but they refuse even I have a proof of them selling overprice stuff. I think I have right to defend myself from being take advantage from the store. I would like to review this illegal crime that Cohen's Fashion Optical selling overprice health care service and reject to refund the consumer when the good/services not as expected.