I correctly understand that your own account at Stake has not do a level 3 and 4 KYC and thus eliminates the possibility that they keep on rejecting your cousin's document because the data clashed as the document already used to verify yours?
No, bills are sent on data and all details for person who is holder of account, that is not problem
Problem is that they dont want to accept documents, simply
Noted, so we can safely cross the possibility of them rejecting the documents being submitted simply due to the document clashed with their preexisting database, namely you already used it to verify your own account to level-4 KYC? Or perhaps someone else on the house already use the same document [by same, I didn't mean the exact same, just the similar documents with different date of issuance, but still the same ownership, nonetheless] for their KYC?
They simply don't want to verify the account and withdraw the money, it was crazy to try anything else.