IANAL but you've paid. The money has left your account and it should have arrived their end when the transaction completed. It is their own fault if they've "lost" the money in their POS system. Are they really allowed to turn up and take back their goods if they believe you've not paid? o.O
I don't think they have actually lost the money, It's there in an account somewhere. It's the store's bookkeeping that is out of whack. This is a problem for their IT dept and the BB accountants.
Tracy is far to low on the food chain to worry about.
I've gone on the Best Buy web and filed a complaint. Doubt it will do any real good.