If you mail it back, make sure they agree, in writing, to waive the $8.99 return fee and to cover your shipping costs. Keep all the records from shipping it. Then, if they don’t refund you in a timely manner, chargeback.

Alternatively, if you tried to return it in store and they refused to accept it, inform Gamestop that they’re in violation of their own return policy and ask whether they are able to give you a refund, mail you a replacement copy, or if they would prefer you to pursue compensation through your bank. If they don’t do either of the first two then that should be sufficient to justify a chargeback, too.

I recommend email for your communications with them since that creates a paper trail. Their customer support email is care@gamestop.com

Good luck!