The cam and balance shaft belt and the tension and idle wheels have been a weak point since the introduction of the 16 valve engines and the subject for numerous service bulletins and part updates. For a long time (until 1998/99) Service books stated change every 120k km/72k miles service which, according the service intervals being once a year or 20k km/12k m, means when the car is 6 years old. This was quite irresponsible as the tension wheels (even updated ones) disintegrated long before these limits was reached and must have cost Alfa a fortune in warranty claims.
From 1999/2000 the Service book added a belt check at the 60k km/ 36k m service (or 3 years), which in effect means that the belts and tension wheels will be changed at this service.
A resent Service Bulletin (a newer may have been issued) states belt and wheel change every 80k km/ 50 k m.
This should mean that Emptie have a claim on the Authorized Alfa Dealer / Service shop that performed the last service as the car then was 3 years or more old and not at leasted checked the timing gear.
Though I sympathies with you, Iím a bit surprised that you, as a 2 year member of Alfa Owner Forum, have missed the numerous warnings about the fragile tension wheels, a subject of lots of entries on the Forum.
The Tension wheels often fails right after startup, in fact I donít think Iíve ever read about a failure when the car have been running for some time.
Good luck getting you head sorted.