If you can't find the code or fix it, then complain to the garage. They should have asked you for the code if they were going to need it, and just returning your car without the radio working is pretty bad. I'd call it unacceptable, but that's because I do 50 miles a day and couldn't live without music...
Punto Mk2 ELX 8v in Teseo Blue with the electric Sunroof and CD changer, doing 50mpg whilst passing down country lanes