Hi sorry to hear of your troubles. First of all the
on the 1.4 and 1.6 engine are completely useless on all engines i've came across i'm amazed Renault can't seem to come on with a modified one.
When did you get the cambelt changed original what date and what mileage? Also what mileage did it snap on and what date?
should not be affected by the cambelt change and at first I would have said it sounds like it has been fitted incorrectly but it would be unlikely a second garage would make the exact same mistake.
You could bite the bullet and take it to a different Renault dealer from the one that originally worked on it and get it plugged in to see what they can find but I will warn you now and
is not cheap. If it is confirmed as that you could go down to 2nd hand route though you would need a few extra parts so that the immobiliser still works ok but it would work out a lot cheaper than it will with Renault.
The black smoke and rough running could also be a sign that the
are away again and I wouldn't put it past them as like I say they are useless.