So the disc must have been damaged already before. Thank you very much,

Hi, My apologies if this issue has been posted already, I couldn't find similar issue. I bought a second hand car in September. The car is just under 11 year old. I was given the "MOTOR VEHICLE REPAIR AGREEMENT" for 6 months. I drive the car only on weekend clocking up no more than 30 miles a week. Until last weekend I drove to Paris. Everything was fine until, on my way back I heard a funny noise on the brake. When I stopped and checked I realized the pad is totally gone and its has damaged the disk. There is no warning nor any sign whatsoever. I didn't contact the insurer yet I wanted to ask for advice what I should do. I believe the break sensor is faulty as it failed to warn me (even the sensors is still off). thank you very much in advance.