Cannot delete contact

My friend used my iPhone to login to his iCloud account to send some emails. After that he deleted his iCloud account from my iPhone... But somehow his contacts are now saved in my iPhone and I cannot delete them! I can delete all other contacts but those don't belong to me, keep staying in my iPhone! Tried to reset all settings as suggested by Genius from Apple Store but unwanted contacts still remain after recovering from last back up... Any suggestion how to delete those contacts? Thanks...