Need help – Brakes broken after major customer service???

Hello everyone, hope to get help in your forum now. I bought a Mitsubishi Colt convertible in June 2007. Now in September 2008 I had a big customer service (cost 420 EUR) Now at 42000 km I drove back to the workshop because of a funny noise and it was found that I had only 50% brake power and all brake discs and blocks were over. This was now completely fixed and I received an invoice of 360 EUR. Well, well i ch am a woman and not really fit in autotechnical matters but in my opinion, can it not be that after such a short time after the Great Customer Service, there is a “total damage” of the brakes?????? I also addressed the mechanic and he only meant that with the large customer service only a visual inspection is made. But the brake bevels were totally rusty and are broken off, that can not happen within 12 weeks or?? Can maybe j please explain more carefully and help me if this is justified the invoice?? P.S: that the brakes have been renewed, so I have no problem and I would pay the 150 EUR for this without complaining, but it is more about working time, because the tires would have already been dismantled at the large customer service. Thank you for EUre help.