My A4 Audi Cam belt spapped at Audi Vereeniging

I drove my A4 Audi to Audi Vereeniging as per appoitment booked. The car went in for Aircon gas filling, but at 15:00 Jackie called me to inform me that my car is broken (when they were starting the car after filling the gas the CAM BELT SNAPPED (WHAT???) The gave me the quote and said they re not responsible i must pay to fix it. how sad that this car has just been from service from the same people.