New cambelt fitted after only 37000 km

I took my VOLKSWAGEN AMAROK with 37000 km on the clock for a normal service. They informed me the cambelt had cracks and needs to be replaced which they did. The service book states explicitly the cambelt must be replaced at 120000 km!!!! They were vary vague on the whole issue and promised to take up the matter with the factory representative. I did not hear from them ,they ignore e-mails etc etc. The bakkie was only 5 days out of warrenty on top of it all!! I demand a refund of R6295.65 and a written statement whether a new cambelt after only 37000km is normal on an AMAROK or not. If it is I will make it known countrywide as only very rich people can afford a VOLKSWAGEN AMAROK. I am used to excellent service on MERCEDES and TOYOTA products. This is my worst service experience in my life!!! The invoice or Document number is ***9. They do have my banking details.