I have not enough idea about gate.io as I think I had only created an account on the gate.io But as a user of cryptocurrency I have opened account on multiple reputed exchange site as well as gambling site and everywhere I have seen option of withdraw/deposit is disable along with announcement. And if still not announced yet it is disables on the deposit/withdraw option. But on this site why they have not disabled the option of deposit.
OP had the same problem with another exchange (Phemex). I saw his complaint in their ANN which means OP is likely the one who led to the problem. I don't think it's a coincidence
If at all OP's claims are true that he made a deposit, I think what he did was make a deposit onto a Luna address to his account that he had already saved sometime back. In this case, he is likely not to have checked the deposit page of the exchange that perhaps blocked generating the deposit address at that time and also had a warning about Luna deposits and withdrawals.
He probably just copied the address from wherever he had saved it and made a deposit, only for the account not to be credited at that time since deposits had been suspended.