Cambelts are a maintenance part with a finite lifespan, so it can be difficult to prove that the failure is a result of a manufacturing fault. The failure has happened before the recommended service point of 10 years/112,000 miles, but there is no accounting for the life the car experienced before you owned it, and as a service milestone is approaching the risk of failure is increased. Some independent specialists recommend changing at eight years or 80,000 miles due the potential risk of failure. We would suggest pursuing Citroen for assistance - you could take legal action, but this may be costly and time-consuming with no guarantee of success. You may also wish to consider getting a quote from an independent Citroen specialist who may provide a repair more cheaply than a main dealer.