Poor customer service

I rate MIT MAK MOTORS zero % due to the service I received I bough a mercedes cls 350 on 23 July on 26 July it gave me a problem of power loss took it to work shop was told that its fixed but gave the same problem within a week again, went back in for more than 4times with the same problem last week the vehicle was brought back and I was told that it's fixed, when I requeste for an assurance letter that the problem is now solved they can't give um being taken from piller to post its very disappointing.