2003 Fiat Stilo Awfull grinding noise when the car is movin

I changed clutch in my car one month ago (well, I paid for it and I was told that it had been changed). During the last month on at least four occassions (three on the roundabouts and one when leaving the North Circluar Road) my car was making an awful noise when I was trying to move off. The engine revs were sky high and I had to put my emergency lights on.
What is wrong with my car? Is it a "new" clutch playing up or something else?