If they actually shipped you the wrong unit and you still have your invoice all you have to do is threaten to sue. Regardless of their return policy if they sent you the wrong product entirely they're obligated to correct it no matter what their return policy is because they made a mistake. You have to be very nice on the phone and KEEP INSISTING on talking to someone higher up, if they keep saying they can't help you just keep asking for their supervisor, get names numbers and keep calling, you'll eventually find someone high enough up that will fix the problem. (Most companies will give in if you make that much effort to complain) The biggest thing is keeping a nice tone of voice and being very patient. Never had it fail on me or anyone I know that's done it.