Firstly I would like to know, was that a KYC requirement, did you read and agreed to their terms before signing up on the platform? If you did and you see that this document they are asking for was and is not part of their terms just in case they would want to claim they have updated their terms, you can proceed to make a complaint with the regulatory body in charge of such matters in your region, cause I'm guessing there should be one who handles such, but to save you stress, if it's part of KYC requirement, you may have to share but be mindful not to give really vital information while you do, personally everything about this is really fishy from both ends away from all that I have mentioned.