Money transferred to unknown fraud account, no help

My Asset of USDT was transferred to an unknown TRC20 fraud account. I deposited USDT on BigOne to purchase a different Coin which was only available at BigOne. I purchased the coin and set the coin on a sell position and waited. After some days later I just wanted to check the status and I saw that my sell-order was deleted and the USDT Asset was transferred to unknown TRC20 account. From the unknown account the money was forwarded to another unknown TRC20 account. The supporter could not help me so I see my USDT as dumped. This is the first and last time I used BigOne. I had no information about the login and the transfer of my USDT and also I had activated SMS and E-Mail Verification and there was nothing hacked on my side. From my point of view there is something wrong at BigOne. An I am not an idiot on computer security.