The Huntercoin snapshot was done based on balances on the blockchain. If your coins were on Poloniex, then they were likely moved (by Poloniex) from your deposit address to some of their internal wallets, and their wallet addresses are where the snapshot CHI have been sent.
It was said at the time and many times since then - the only way to really control your coins and be sure to get your CHI was to hold the Huntercoin yourself. With coins held on Poloniex, it is up to them to distribute the CHI. So far they always promised to do that, but we have no control over if/when they really do it. The best you can do is to open a support ticket with them and ask about it - the CHI have been sent to their addresses already quite some time ago, so they just need to distribute them now.