Closed account and won't pay my winnings

Once I made a deposit from the card to this casino, I received a bonus for the first deposit, but I could not wager it. Since then, I always received various bonuses from this casino on the post. And now, not long ago, a letter arrived that credited 50 free spin into the games of Gonzo Cuest, Twin Spin or the Invisible Man. I used 50 spins, winning from them 50 euros. After I successfully fulfilled the conditions of wagering x35, and the remaining 75 euros ordered for payment on the card with which I previously made a deposit.
I received a letter that they need documents. I sent all the required documents. It took 4 days, wrote to them, asking what was the matter, why they were silent. Answered to re-confirm the address. Did this . Two more days passed, today I'm trying to log into my account and I get an error
Internal error has occured, please contact support

As I understood, I was blocked. But I did not break anything. I do not have duplicate accounts, I did not break the rules of the casino. But they refused to pay money and I was blocked, they did not send any notice to the post even. They just blocked it in silence. And now they do not answer my letters in support.
Help deal with the arbitrariness of the casino and return my 75 euro!

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