The last time I used hitbtc it was on peace, It was in 2017 when I quit using that exchange because I found out that there is a better exchange than them but I didn't expect them to fall too much. I've been seeing different complaints about them after implementing their KYC procedures.
i'm old user of HitBTC too, but today i used to exchange 0.2 btc into 3600 USDT.
when i try to withdraw i got that error. i used HitBTC before with up to 7 btc total. but don't know what happen after a long time. so be careful.
if account verification is required, why they don't ask for it before i invest.
however, for small trader i don't think documents should be required.
I think you didn't read their TOS after depositing that amount. I am an old user too, using it after a long time of inactivity it would be our responsibility to read their TOS again before using it, their KYC procedure is strict and pain in the a**.