CAR SERVICE GONE BAD!!!

MY CAR WAS TAKEN IN FOR SERVICE AND I WAS TOLD THAT I WILL HAVE TO PAY CASH FOR MY SERVICE WHILE IT HAD A FREE 60KMS STANDARD SERVICE AND I HAD TO STRUGGLE TO GET MY REFUND AND THEN NOW WHEN I DRIVE OVER 120KMS THE CAR STARTS TO SHAKE I HAVE TRIED TO SEND E-MAILS TO GM MOTORS BUT NO ONE IS RESPONDING TO MY WORRY FOR MY 1ST SERVICE I FEEL THIS IS NOT BEING FAIR TO ME.