I didn't have any problem with verification in Bittrex but that was 2 months ago. But then when I lost my Google authenticator when I changed phone, I asked them to reset my 2FA and sent a selfie of me holding my passport and writing on a piece of paper the word Bittrex and the current date. I got my request fulfilled in a couple of hours.
I can only assume some lack of info on the submitted requirements or they may be having congestions on their support tickets.
I would try sending a new set of required documents and make sure to follow their instructions to the letter. Hope this helps, somehow.
My sister got a passport so hers was accepted. I only got Philippine government-issued PWD (Person With Disability) ID. It is depressing.
That's probably the reason why the delay. Maybe a postal ID will help. Definitely passport is their official document requirement. You may call their tech support number, which is way faster than just a support ticket.