BMW so called car service

I took my car for service at the BMW fountains circle end of November. My car was in good condition when I took there it was just due for service. When I started driving the car, the car started to have a burnt smoke coming from the exhaust...it smelled horrible. When I took the car back ,before they even checked the car, I was told that it could never be their fault. As there is no way their technicians did something wrong. It is odd that just after the so called service, my car had to do that.