Master Auto Body

I was hit leaving a scratched and dented rear 1/4 panel . I wasnt worried about the dent only the scratch which could rust. I explained this to the tech. It looked good, but 2 years later the scratch started to rust. I took it back. They said this time they will take the bumper off to access the rust under the lip of the panel. Why didnt they do this the first time? Again, 2 years later, the rust is back. Do paint jobs only last 2 years? Very disappointing.