Sorry, I can't follow your question. How much did you actually pay, for how many cans?
Companies can be liable under the DTPA (Deceptive Trade Practices Act) for false advertising. Ads are not generally considered an offer, just an invitation for you to offer to buy at that price, so there's probably not a contract at the advertised price.
Of course, the other critical question is - how muct time and money are you willing to spend to pursue a $400 refund? Filing suit will definitely not be economicaly feasible.