I have used mxc for only 1x transaction which is quite decent and still safe, it's just that after I saw the review on google it is indeed that exchange that has a bad reputation because a lot of people complain about problems like what you are experiencing, but your mistake is Coinall and exchange which similar to mxc and in my opinion much worse and seems like nothing can be done to get your GRIN Coin back, sorry to hear your loss.