I've been using Poloniex for almost 1 year now and I have no problem relating into this. It seems that they are just being skeptical because you have a big amount of holdings so your verification must be fully comply first. It is true that their support sucks most of the time in responding to their users but they will resolve this case if you follow the rules. I know it is frustrating to wait but they will not steal your coins and you must document everything for your evidence just in case it worsen.

I once lost my mobile phone and my 2Factor Authentication is there and I contact their support to disable it for me to access again my account and they resolve it for more than 2 weeks because they are requesting too much information for my real ownership and that's fine with me for as long as they restore it.