VW Golf Sunroof explosion

Absolutely disappointed with the service I received from the the Centurion VW Autohaus. I was driving on the highway when all of a sudden I had a frightening experience when my sunroof exploded. I had driven to them, the service manager and a technician checked the car, and advised me that warranty cannot cover this as they "feel" this may be caused by a crack or stone chip. They could clearly see there was no chip, or point of impact etc. I logged this with VW SA and a lady Mariam assisted. She was great, but unfortunately she didn't get any feedback the Centurion. She advise that there was nothing she could do and sent me a letter apologizing and closing the issue. I requested an assessment report as well the inspection report which up until now, I received neither. The letter states I must contact the branch directly. My car is a VW Golf 8, and still under warranty and they have just got away with this. Will never be purchasing another VW again.