How do I get my money back if the van I bought is defective?

I bought an ada van for 13000 and paid 5000 first time, 5000 when vehicle was ready. But the problem is from day 1 check engine light is on. Guy said it's false code nothing wrong with van and it's registered and passed smag. He said it's computer problem, changed today but as soon vehicle entered in my parking, C light comes again. I run the car fx report and found that meter is tampered .70000 less showing on meter than report. I told the dealer guy I don't want it. I need my money back but he is always like we'll fix it this and that. I told him to lower the price for 1500 but I still need to pay the rest of the money. I told him money back or fix it. But after 20 days, same issues. He used his company later for sale documents. Can I call DMV or what department for that issue? He has original documents under his name. Please help.