Yes it is a cloud mining service. I lost around 0.5 BTC. I can see people yelling on their Twitter/Facebook, I trusted them because they WERE owned by Bitmain. And later I realized Bitmain was no longer affiliate with Hashnest. Such a terrible moment
Considering the price of BTC this is a good amount you lost.
I have seen many fake websites to use the name of Bitmain and later they were caught as scammers. Not really sure what happen in your case that if indeed they were owned by Bitmain. I am wondering why would Bitmain would need a cloud mining business at all?