IM IN TROUBLE WITH MY 360...!HELP WHAT SHOULD I DO?

Okay so i recently bought a 360 a month ago and my warenty ended last night..i asked them to sell me a used xbox 360 [PRO]!!!! for 200 bux and they said okay..but instead those Asian basterds..sold me a xbox arcade with a hardrive for 200 dollars and its a used 1 when a new 1 is worth 200..What should i dO?!?!??! panicking.