Ugh, it's scams for amounts like that that make you want to jump out a window, and I feel for you OP.

I've heard of HitBTC but didn't realize they were so notorious as scammers.  And asking who you got the bitcoin you deposited from?  That's just a ridiculously over-the-top addition to the KYC requirement, which they probably figure will force the average person to just give up and go away. 

Where is HitBTC located, anyway?  Somehow I have a hard time believing whatever government they're operating under is requiring them to get KYC documents from their customers.  I have an easier time believing that whatever KYC info you give them will end up for sale on the dark web.  Good luck, OP, and fuck these scammy exchanges.