Brakes failed after new brake pads and discs replaced

I had new brake pads and discs replaced, also anti roll bar at a garage on Saturday. I picked up my car late afternoon and drove the couple of minutes home. Sunday I used the car and drove a twenty four miles the car felt weird right from when I set off. There was grinding noises and felt like the car was pulling to the side. Also felt like I had to plant my foot to the ground to get anywhere. My partner said it probably felt different due to the new parts on the car. So I carried on driving but carefully. On the way home about ten minutes into our journey I heard really bad thudding noise and the grinding was getting worse by the minute, then could smell awful burning smell. I tried to pull over but my car was not stopping anytime quick the noise was horrendous, by this point I was really scared with two of my five kids in the car and very close to a ditch I thought we were going to end up in the ditch. My partner used the handbrake to stop us. We got out and upon checking saw the caliper hanging off. Straight away we called the guy from the garage he came out about one hour later and straight away told us there was no bolt in the caliper apparently it must have shredded off and dropped out. The mechanic drove my car roughly fifteen miles back to his garage. I got my car back yesterday and was really scared to get in it I am struggling to get the image of the car not stopping, and the what if out of my head. :( I asked the guy once again, when I collected my car what had happened and why it had happened to be told that it is a common thing with brakes. Bad one happens probably one in every fifty jobs that are done the bolt just comes loose, it is no ones fault just one of those minor unfortunate things. I am now more worried than ever as worried could happen again and be a lot worse if this had of happened a few minutes later I would have been on a sixty mph road and I really do not think I would have had any chance of stopping. Luckily when I pulled over I had just came off a round about and was going slow. Upon talking about what happened, my dad's friend told me this should never happen it would not just shred/fall out so quick after the garage had done them unless they were not correctly fitted and the garage is lying to me. He said the garage failed to check work done and had in fact forgot to put the bolt in and sent me and my kids off. I do not know much about cars but feel this could have been so much worse and is constantly on my mind worrying. I suppose my question is are the garage lying? Is this just something that happens or is the garage at fault? I feel as though mine and my children's lives were in danger and not wanting anything from the garage but if it is their fault/neglect that I need to report as brakes are very serious and would not forgive myself if it happened to someone else. So for the long essay, any advice small or big would be very much appreciated. Thank you for reading.