Having work done on your car shouldn't have any effect on what the radio code is. Are you quite sure that you have entered it correctly? Where did you get the radio code from? If it's written in the handbook someone could-well have fitted a different radio at some time.

Failing that, you will need the serial number that's printed on a label which will be either on the top or the side of the radio. Probably starts with "M" followed by a six digit number. Radio needs to be pulled out from the dashboard sufficiently to read this label. You don't need to disconnect it, just pull it out far enough to see what the serial number is.

When you have the serial number then please post here again.

If someone has fitted a different radio at some time then you might even find the radio code written on the case. This happens sometimes.