Ouch!
How many miles you done and does it have FASH?
Had a similar thng happen to my first Corrado (16V). It had been for dealer service and I'd asked them to change the cam belt as it had done 52,000. When my wife picked it up they said no need for the belt as the interval was 80,000, it failed a few months later at 56,000, same thing, 8 valves and 4 pistons. Dealer initially refused to pay as the previous owner had missed one service so they say mileage cannot be verified (?). After reminding them I had asked for a new belt at the last service VW agreed to supply parts at cost and labour FOC. Then they paid a sceond time after making a rough job, dropping a bolt into the belt cover which wore through the new belt, broke it and repeated the damage after just 400 miles!