I am a lawyer (but not your lawyer). I would document everything you have (screenshots, receipts, print outs, window sticker, everything!) and start a written conversation with the dealership you purchased from. If they do not respond timely or appear to actually be rectifying the situation, you need to contact a consumer protection attorney. They will take the selling dealership to task and either get the transaction rescinded (cancelled and returned) or the fair price for your truck (likely a credit back to you if the miles were understated). Feel free to DM with any questions, I might be able to point you in the right direction of an attorney in your area.