Good luck buddy, as something's ground the belt down due to error of fitment imho!. This happens to a fella tt owner with a brand new belt kit and in the end his scrapped his motor and bought an S3. Not saying you need to scrap your motor as he's one went with a bang 
So, you were right! There was an error with the cam belt fitting, a bolt had fallen out and done the damage......
The garage have been very apologetic and refitted the whole kit and dropped the sump and cleaned it out too.
Running fine now, pulls as it should.
Was a relief that it was caught before it went pop!
