Who has the worst support in industry? My vote is for polo.
1. Poloniex
2. Yobit
3. Coinbase
4. Changelly(though their customer support is actually quite active, but there are just so many issues).
I must have to agree too that yobit is the worst support ever than those mentioned sites, their support takes weeks and even month/s before they contacted you back with the support ticket you made thats why you need to avoid this exchange so you can't experience what others did before. 
Yobit has definitely never been above median for customer support, and nor have they improved over the years even though there are hundreds if not thousands of accusations opened against them for crappy customer support. But, poloniex right now is on a different level. It's evident that they are trying to end all communication between the staff and the customers, by removing the trollbox, delaying withdrawals and deposits, customer support never responding to anything. At least yobit is willing to take on new shitcoins for a fee, poloniex doesn't even open new markets anymore.