Did you send them screenshots of the actions you took using these funds in chronological order, for example (purchase, exchange, and transfer,) before sending it to the HitBTC platform? And the screenshots you provided must be full-display and contain transaction details such as the hash and the address as well. As they mentioned, you have to send them screenshots of your withdrawal history in the exchange through which you transferred and withdrew the funds to the HitBTC platform, and I hope that your problem will be resolved after that, frankly, HitBTC is an unpopular and bad exchange platform, and they have procedures that make us put a red flag around it. Fortunately, I haven't tried it before, but I have seen thousands of users who could not pass the strict procedures imposed by the HitBTC platform about determining the source of funds.

I think they are asking for source of your coins, not source of your fiat money
That means you need to explain from what wallet you send coins to HitBTC exchange, your own non-custodial wallet or from some other website/service.
I hope you don't have lot of funds stuck there, but my suggestion is to stop using any centralized exchanges and transition to decentralized exchange like Bisq and p2p trading.
I heard bad things about HitBTC before, just do a quick search and you will find a bunch of bad reviews and complains on internet.

Maybe, I don't know. I never tried. Or maybe someone can go after their domain name.

They want to keep your money.

Can you please tell what are the documents you provided to them and they rejected it? If its in the form of fiat then bank statement is enough to be considered as valid source of income while if it is crypto then its kind of complicated but proving the address history and how did you made that with enough evidence is good though, if they still not helping to complete the verification then there is no actual way.

Do not use HitBTC, they have high transaction fee and they do seize users coin or freeze users account, asking the user to provide KYC documents.

Normal documents like driver's license, national identity card or international passport. It has been long I used the exchange, because of high withdrawal fee and when many people are complaining about freezing of their account.

The OP did not mention if he had deposit the money at the exchange. When you upload the data (KYC), on the site, they can still sell your documents to anyone without knowing you and without banning your account. There is no need to ban your account in order to misuse your account.

That is the reason that we should only do KYC at the trusted site, otherwise our privacy, our data can be misused and in some cases, we never know where our data is being used for unlawful purposes.

HitBtc exchange is a very shady exchange there have been many accusations about this exchange you should be aware of it.

You can see from searching about Hitbtc on this board : https://bitcointalk.org/index.php?action=search2

So in your case, you make a deposit and then Hitbtc asks for the source of the transaction until it's gone through with the documents and Skype is still on hold?
How much money do you think was robbed?

Очередной набор верующих.  Только из за битка курс полез.  

Рекомендую почитать в гугле " Как криптовалютный рынок обманывает инвесторов" сейчас везде эти новости есть. 

Цель у кукловода или разработчика сделать его богатым или знаменитым. Всегда думайте за чей счёт банкет. Тогда проще принимать потери и не включается жадность.

Многие порно студии в великобритании продают доступ за битки. Получает Ваша идея это уже апгрейд того, что имеется