I have seen Poloniex more than any other exchange have exactly these kinds of issues. I am not launching any accusations, but it seems, (at least anecdotally) that this is a very regular occurence with this exchange. I have seen high ranking members having similar troubles; if I am not mistaken (please, correct me if I am), BAC has had similar issues, but once support gets involved this gets remedied. I have not seen anything like this go completely unanswered or unfixed.
They have been having a lot of issues recently with withdrawals and deposits alike, which I imagine has filled up their support queue and backlog quite nicely.
https://twitter.com/Poloniex/status/961030372967550976Many users are complaining about their deposits going without credit into their account.
https://twitter.com/Poloniex/status/961102960011997186They say everything is working normally on this status, but there are many users freaking out if you read the comments. The one fellow mentions that it took 6-months for him to get a response from their support, but then the problem was fixed.
If this is a systematic issue, I wouldn't be surprised if they did this purposefully to offset their own investments/trades or potential exit-scam. This kind of thing is normally a prerequisite to an exchange going AWOL, experiencing a "hack". I've just seen it happen too many times before, but hopefully they are different and do not disappear for one reason or another. It seems like you just must be patient, and I would suggest again bumping your support tickets at all, but especially with things like "I'm waiting!" as this normally resets your ticket's position in the support queue. The best advice, would just be patient and if you can try to contact them on social media as that has worked for a couple people.
Also, if I could make a suggestion, try to (if you can) move your coins into your personal wallet from the exchange before moving it to another exchange; there is sometimes weird things that occur when you do exchange>exchange withdrawals>deposit; not sure if this is intentional, maybe to thwart arbitrage, a fluke in the programming, but normally you are better off going Exchange > Personal Wallet > Exchange if you must do so at all. Exchanges inherently come with these problems all the time, there are so many ghost stories around the forum of exchanges stealing this and that, not crediting this or confirming that; I would also advise against using exchange in any capacity you can.