Best Buy return gone wrong

So I wandered over to Best Buy yesterday to attempt to return the dashboard mount for my GPS that I got for Christmas. I would have kept it but the suction cup that's included with it worked so well. Anyway, I wanted to get a store credit because my parents told me the thing was worth like 40 bucks, so I thought BONUS GIFTS! Well, I stepped into the store, waited like 15 minutes in a short line, and finally was called over to the customer service desk. I showed the woman helping me my receipt, and she scanned my dashboard mount. After scanning it, she told me that it was already returned. I thought for a second, and then I told the woman, how could I have returned this when it's in my hands right now? She told me to wait a second, which turned into ten minutes. Standing there with my friend, we began to count the number of obese people working at the store. It turns out that the proportion vastly outweighs those that are skinny. She got back to me, and said once again that it was definitely returned. I told her to hold on, she told me to step aside, and I proceeded to call my Dad. I remembered my sister returned her GPS dashboard mount the other day, and it occurred to me that she got my store credit. My parents bought hers during Black Friday, so I would have only received $14.99 back, in addition to being forced to pay a $3 restocking fee. Not an option. I left the store, dashboard mount in hand, still angry. I wrote a nasty customer satisfaction survey, and I'm going to make my sister fork over my Gift Card, after giving her a copy of The Hangover that my friend gave me.