Bitcoin_Arena is correct when he says that an announcement was made that deposits and withdrawals will be suspended 4 days before OP sent those coins. But as okorieemmanuel rightly said, users of Gate.io shouldn't have to go search on Twitter or Gate.io articles whether or not they can deposit, withdraw, or trade their assets. Such instructions need to available on the wallet page which shouldn't allow you to display a receiving wallet at all due to a suspension in trading.

When it comes to accusations of the exchange doing arbitrage trading, that has to be proven and I doubt OP can do that.