Hi Brian, I personally would have been suspicious of the brake discs having been damaged, I may be wrong but that error of doubt would have lent me to a second opinion. I would also change both tyres on a axle to such an event even though there was nothing wrong with the other although I would insist on keeping it for spare if the rear were the same. I do suspect the DSC light issue would be down to the garage having taken the discs off to replace.
One thing I would have done for sure is request the so called damaged discs that were replaced to obtain an expert opinion with the likes of the RAC/AA etc. If they then found them to be OK then I would refer the matter to the garage who undertook the work and request compensation, if they would not oblige then I would be taking the matter to firstly Trading Standards then the County Court for damages.