There is a notice and a warning which is shown in this reply :
So I think it is not right to attach credibility and reputation here, since it is the user's fault that he sent the fund to the wrong address. The most the Duelbits can do here is to consider the request but they are not obliged to do so.
I still hope that Duelbits gives consideration since the amount lost is not small.
All clear, there are warning notification about TRX address deposit fund available for TRX coins only not for USDT with TRC20 network, I think its fatal mistake from OP because Duelbit have warning based on above picture. I think have winning solution between OP or Duelbit teams about refunded if any possibility but OP need to pay refund service fees based on happening when sending in exchange wallet but we use difference network kinds and still not supported yet in exchange market.
For every one before depositing fund in gambling platform account see their term of service, which one network allowed and supported for depositing because not all exchange will supported all network for depositing our fund.