Is Poloniex SAFE to trade? Is it a scam exchange platform?

1. On 4/6/16, I transfer my Steem Coin form Coin Payment to Poloniex, Coin Payment reply confirm transfered

But I idnt receive any at Poloniex,

I create ticket to poloniex on 5/6/16, but unfotunate no reply

after that I almost everyday send reminder to them, but dissapointed that until now(1 months time) no reply.

1. I had some EMC coin store at Poloniex, 4 days ago, EMC2 coin is suddeny frozen by poloniex for trade without any reason( but in Bittrex can trade),

Same, I send ticket to Poloniex, but no reply

I personally VERY VERY DISSAPOINTED to poloniex, how about you?