It would take a lot of abuse or riding of the clutch pedal to get a failure after such a short time, however with persistance it can be done!

If your dad has not had a short clutch life with any previous car, then maybe a mechanical fault in the clutch assembly has caused it to fail.

I think without you managing to get hold of the failed assembly and getting it independently inspected, you'll have an impossible job of proving it was. I don't think there is a chance that the dealer will change their opinion without this.

Well, you are going to need the clutch replaced anyway so when you do ask to look at the old parts. If the friction material is worn out.....then your dad has done it. It's easily doable especially if the person has bad hearing, because modern engines are quiet they can't hear how high they rev the engine whilst slipping the clutch, if he rests his foot on the clutch whilst driving that will add to the problem.. We sold a toyota Yaris to a dear old boy who was as deaf as a post, he burnt the clutch out in 500 yards ( 7000 rpm clutch slip out the forecourt and down the road to the level crossing waiting for a train).