The standard VW Cali picnic chairs are fragile, uncomfortable and ridiculously expensive for what they are.
If the car is in warranty then VW will replace the whole chair which given the nature of the fault, is ridiculous? I've had two or is it three replaced? If not in warranty then my advice would be to source the metal replacement joints that are available and replace them yourself. Check other threads on this subject for details of where to source them. Once replaced or repaired place the chair back in the boot lid storage and forget it. Next, buy yourself a pair of stronger, cheaper and much more comfortable picnic chairs. There is so much choice in this field and most offerings are miles better than these over hyped chairs.