If you financed through the dealer (which I think you did to receive all of those incentives) it seems they have 10 days to "finalize" the contract and can legally rescind it within that time frame.
The 10-Day Rule: When can sellers cancel a car dealership-financed contract? Have any questions, please contact Auto Fraud Legal Center.
www.autofraudlegalcenter.com
If you self-financed tell the dealer to pound sand. They were already paid.
And no, if you sign a new contract for $2500 more they won't care about giving you any incentives like free oil changes unless that's their standard contract item. But it doesn't hurt to ask.
Used car dealers use this scam all of the time. They want "to get you into your new car today" and will do anything to do that so you sign the contract, drive it home, get attached to your new hoopty, and want to marry it. Then a few days later (they have 10 days), after the wedding, they say your financing didn't go through and you'll have to sign a new, more costly contract to keep your new spouse.