motonovo voluntary termanation with engine damage!!!????

[myname1]

hi I hope someone can help, we have a car financed with motonovo and we have payed 69% of loan, the car has been well looked after regularly serviced and hasn't done exsesive millage since we bought it (10000 miles a year) I would like to do a voluntary termination and just hand the car back my issue is the engine has started to make a knocking sound and ive been told the cam is knackered in the head of the engine the cost to put right will be in excess of £1500 we have just spent £1100 0n replacing the turbo and I just don't want to spend anymore money on the car as its not cost effective and the car is not worth this amount of money, please can someone advise if and how I can vt this agreement. thanks in advance.