Holden Astra 2002: Timing belt failed after service

In April last year I had my 2002 Holden Astra City's 120,000 km logbook service done by my Holden dealer, during which the timing belt and tensioner were changed for the second time. Just eight months, less than 5000 km later the timing belt has failed. The reason for this is that the water pump bearings seized. The water pump was replaced at 68,151km in 2005 along with the timing belt and tensioner assembly during the 60,000 km service. My Holden service centre is asking for $420 just to have a look and assess the internal damage caused by the failure of the timing belt, and at this stage is indicating up to $3000 to fix any damage caused. What use are the recommended manufacturers? service schedules if this kind of thing can happen so easily and with such devastating consequences?