I know that poloniex might be the 'biggest' exchange, but one month ago when i actually got started with cryptocurrency, i had to open 2 tickets with poloniex and it took 10 days to have the issue fixed ! I am starting to avoid using it as much as possible, it might have the most trades, but if there is an issue, prayers wont be enough :D

In my case , i was sending steem to steemit and was transaction in error, and had to wait 4 days to get a reply and 10 days to have it fixed.