Do you have all 6 C relics? And do you have a C7 already that was gifted to you by someone else?
If you don't have all 6, you need to successfully get C1, C2, C3, C4, C5, and C6, in order for it to convert into C7.
If someone gifted you a C7, you have to get rid of it/trade it to someone else, you can't get the title if you don't remove it from your inventory.