If the mechanic has put it 'on the wrong tooth' then he has buggered up the timing.
I wouldn't mind betting the mechanic didn't have the proper Ford timing tool to do the job and just locked the cams off as best he could.
(The proper tool fits the camshafts to stop them moving relative to each other during a cambelt change. If you're very careful you can do the change without it, but very easy to cock it up)
Ask if he has "the tool" to do the cams. If he doesn't mention a special tool to do it, then tell the mechanic that he should have one or else it's very difficult to get the timing right and it'll run like a bag of spanners. Then say that as it's commonly needed to do it, that will be the reason it's running crap.
Just the fact that it was running fine when it went in and ran crap when it came out can only be the fault of the garage. Don't take any fobbing off. Mention trading standards, MOT / VOSA approval if they are an MOT test station and council departments to get the job done if need be.
Good luck.