Can't login to iMessage because of wrong serial number
After a logicboard and keyboard change, the technicians at the service flashed a new serial number to the board that doesn't fit the original serial which is on the box. After upgrading to Mountain Lion a year ago my iMessage stopped working with Facetime. As well as iWork documents don't sync to iCloud from my Mac. I didn't realize this till recently as I was using upgrades from my old system but when making a full new install that problem occured. Is there a way to fix this problem? When I asked the technical service they insisted that a flashed logic board can't be flashed again.
MacBook, OS X Mountain Lion (10.8.4), MacBook5,1 C2D 2,4