Nissan refused to exchange car.im stuck with it i cant sell it either as the settlement is too high.I NEED HELP

i purchased a Nissan Qashqai in 2017 it was used.it wsa on 32000km. I only enjoyed the car the first 3 monthsthere after its been hell. I sent several emails to nissan rosslyn plant but to date derived no joy.Ive been tossed from pillar to post.each branch ive been sent to detects the same problem but cant fix it permanently.The start and stop pops 'cant detect key'i have to devise means to get it started.worst still it happens even when the car is in motion.at one time my car was booked in for 5 weeks to attend to the problem im still experiencing the same .what should i do