You didn't give details how you lost the BTC. is it that you sent it and it failed to be deposited or your account was compromised? I have an account there but will never trade there due to poor support reviews, coupled with high withdrawal fees.
my deposit was successful and I started trading there but after 3 days my balance suddenly disappeared, I checked history and no transactions came out, this is very strange right!
Just try to take a direct conversation with HITBTC admin on telegram group. I hope your problem will be solved as soon as possible.
I have joined and asked the admin there and their answer is the same "please send support"
I've given up and maybe I should forget the rest of the money is there now even though it's pretty big around $70
my advice for everyone to stay away from hitbtc so as not to have problems like me in the future