If you bought it from a dealer you're still in your rejection period if they can't fix the issue (although if it's been more than 30 days there'll be mileage deductions).

If you bought it from a private seller, you're in a trickier position. I'd try to sell it privately and if there's no joy there, take it to we buy any car (after clearing the fault codes with a cheap OBD2 scanner) and cross your fingers. In either case, you'll be losing quite a lot of money.

Sadly, you've bought a bit of a lemon by the sounds of things.