If you bought the game from forummer, this means the said CD key already used to create / attached to a Battlenet account.

If blizzard asking for identification documents, you need to provide the ID that matched the previously registered information. E.g. If Mr. A created the battlenet account using his name and so on, you make sure Mr. A sent in his IC and not yours as this will led to permanent ban during buying / selling accounts which is prohibited by Blizzard.

My advice to us is ask the seller to do the necessary to unlock before sending it back to you or he willingly to scan his IC and driving license to you. Or you have all the rights to ask for refund. You bought items that cant be used.