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So, it's not a scam.
You're just not completed the document they're asking, It's on their term & condition and you cannot blame on them as well. Becasue it's part of their service rules, proof-of-source fund is always tricky for people like you. Your account still temporary locked and can be opened, but with condition finish the document first. If you keep asking, and not completed the document it's just wasting their resource time. Try to submit, and contact them again not just keep spamming communication.
Still cannot find the alternative for this one, I only got alternative for proof-of-address if people are still living on their parent and all the bill under other name not us. Did you pay tax in your country, If yes then tried to submit that. You never know, it can be accepted or not.
Are you acting naive or actually are you? I played with money that was not earned from BTC mining, which is the only proof of funds they accept. My proof of address, identity and everything else is verified.
I had a very similar problem a few years ago with cex.io, they asked me for proof of funds, I confess that at that moment I was very confused because I have a verified account on cex.io since many years, so I took some time to think about what I would send because the money came from the casino and I hadn't read the cex.io TOS, but I was honest and made a print screen of all my transactions from my casino account, including my full name and proof that my casino account it is a verified account and the funds i deposit in cex.io always come from the same place, i sent them all transaction ids from casino account to my cex.io account
the response I got from cex.io was that that's all, but that I should no longer be sending funds directly from the casino account to the cex.io account, I should send it to my wallet and then to the cex.io account, and I I always use the same wallet address to deposit at cex.io
With this story of mine I think you must have already realized where I want to go. you say you do mini jobs, so take a print screen of all your transactions along with your full account name from where you receive the coins, take a print screen of your wallet, and the transaction IDs so they can verify that the coins you deposits come from place X,Y and Z and arrive in the casino account.