Poor service delivery

For past 5 years, I have been taking my car to them for service, I have never skip a service or change the service provider. Then only to have car having a cam belt break and breaks all the valves. When I enquired, I was told it was changed on 150000km and currently it's sitting on 215000km, so it broke just after 65000km. Either it was not changed as claimed or poor workmanship. Very disappointed to incur extra cost, I was trying to avoid by taking to the official dealership.