this could be the obviuos answer or may be there is more to it
Delete the contact name in the phone then try again
ususally when this happens the contact name is in the phone MORE THAN ONCE
some times you have the surname and a 1st name ie 2 entries but the same number in this case the phone can not display a name
You may also have the name on the sim and the phone the earlier nokias could not display a name when this happened but the later ones are able to cope UNLESS the there is a conflict name spelt different on phone to sim again the phone can not cjhoose so displays none
Try deleting the offending name and get to call you again
or delete the name THEN key in the phone number and press dial see if the name appears which proves there was more than one entry
Nokia user / modder since Nokia Orange and Mobira user too before that