Have you checked your litecoin deposit address or transaction in litecoin blockexplorer? If you can see that there and still can't see that deposited at your hashnet account than you should contact hashnet support rather than poloniex.

But if you can't find your transaction in explorer than you might have to wait for months to get answer from poloniex support.

If your transactions is not confirmed (6+ confirmation) than wait for it to get confirmed.