S60 (Symbian)

Check to make sure that the contact is listed by name, and with the right number, in phone memory, and not just on the SIM card. If everything is already in proper order there, and you are still having the problem, then check all of your call and display settings. If everything is correct there, then run a diagnostic on your Symbian software build (there are S60 apps available out there for that kind of thing), and if it finds a corruption then you could try reinstalling your version of Symbian OS using the software update tool in Ovi Suite. I imagine you will find the answer in one of these steps... if not, then I don't know what else could help at this point.