mastercard

I had my card number stolen and it was used for almost 2000.00 of product at Chico’s in Las Vegas. Washintonton Mutual is telling me now that they did not receive my claim forms in time, that they closed the claim and that its over. I need to know what is the time frame in which I can hope for help from Mastercard. What are my other options? To sue the vendor? Or am I just out thousands now?