Car repair

Good Day. I took my Nissan Navara to Nissan BB in sinovile 3 months Ago for them to reset an enigine light on the cluster but the called me and told me there were a couple of things to be done on the car and billed me over R13000 and told me I have 12 months guarantee,after 2 weeks the car started to smoke non stop and and the car has no power at all which intially was what they were suppose to have fixed,now they tell me they need to open the top(enigi e)and it will cost me R5000 just to open the car. Can you please help,if they can pay me back my money so I can take it somewhere. Car reg FZ25JSGP(Nissan Navara)