Bethesda no longer supports Oblivion, so PS3 users are kinda screwed when it comes to this bug.
There is one possible solution: http://www.uesp.net/wiki/Oblivion:Vampire_Cure#PS3_GotY_Vampirism_Cure_Notes Other than that, if you want to ditch your vampirism, you'll either need to start a new character or reload a save from before you've become a vampire.