Traction problem and black smoke

I bought the car new, there was a dripping in the 1.4 diesel injector, it was fixed, but now I am facing black smoke and low traction, they said the problem was in the turbo, they said to have the turbo revised, but I couldn't trust the mechanic, the guy touched the car, the turbo went off, I didn't like the workmanship he did, who suggested an idea?

Has anyone experienced a problem like this before?