But yes you may be got phished if you clicked in some emails or something ...
First of all, the address where you deposited the Bitcoin into Nucleus is not the address that will send the coins to Alpha. They will be drawing the coins from other addresses, so it is unreliable to watch that address. Instead, watch the deposit address and see if that had received all of the coins. If it did, contact Alpha's support, there is nothing we can do about it. If it received nothing, then check your withdrawals and see if it went to the right address. If the bitcoin went to the wrong address, you may have been phished or you have the bitcoin address changer virus.
It would be helpful to know what the deposit address to Alpha is.