I already opened another ticket in January. But still no reply
Yeah, that was January and it's already March. That's long enough to demand a reply for sure. You should open a new ticket again for sure and hopefully they can attend to this matter as soon as possible.
Missing deposits seem to be pretty common with poloniex. But you have proof that the deposit address works with your second deposit of 20~ USDT which went through without any problems. That should simplify the process of solving this.
But first, poloniex needs to respond to you and that's what's not happening. You really only have the option of waiting and opening new tickets once in a while. Their support consistently this bad, which is the reason why I've stopped using them ages ago.