what would l get if l return it to the dealer because l already payed off about 12,000 dollars. what should l do?

Nothing. You need to call the people who loaned you the money and work some thing out. The dealer sold you the car they did not lend you the money. Do it before they call you.

l would say to try to sell it yourself first on some where like craigslist or autotrader.com If you do not get any bites you could try to sell it to a dealer however you may end up owing more than it is worth.