Scammers disguise themselves as a stock exchange. When you deposit your money, they block your account, ostensibly to check documents, while any documents sent are answered with "photo changed".
In the support service, there are most likely robots who always answer either "you still need to wait" or "you sent the modified photos." I believe that such an "exchange" should be blocked on all resources, such as Coinmarketcap.
Most platforms ask nowadays for KYC. Some are legit, some are scam. Some of the legit ones have badly configured system for handling KYC and in most cases the support answers slow (if at all).
I don't know which is the case for HitBTC. They are pretty old on the market and I don't think that they could have been surviving if would scam for so many years.
My advises would be:
1. If you indeed want to use a (any!) KYC platform, you better ensure you have passed the minimum KYC for withdrawing funds
before depositing anything.
2. If you have problems with them, learn to have patience. It's nice that you've warned us (and I do appreciate that), but only their support can help you for real.
If you've used only their chat, you should try to open a ticket. If you've got automated answers on tickets ask farther until you get clear answers on what to do next. And keep in mind that unfortunately not all support employees are smart and helpful.
If indeed it's getting proven that they withhold user funds without good reason, then they'll get - sooner or later - delisted from the various platforms. But for now (and sorry if it sounds harsh) your only "proof" can be read as "your papers are not 100% right and you don't have the patience needed for this".
PS. I've had account on HitBTC many years ago, I didn't like the platform to stay, but I've withdrawn my money easily. Just it was before the KYC days.