Don't panic. Yet. This may take some time. It may fail. But worth a try.
IMPORTANT UPDATE : one of my friends went the letter route - below - a couple of weeks after being hacked. IT WORKED!!!
If it fails or X support is not all we would wish it to be, you can use your downloaded archive to start over, contacting all your Mutuals and asking them to boost you. If you have your archive. If you are in the fortunate position of reading this BEFORE you have been hacked, get it now. See the home page for info.
Never pay anyone claiming to "hack back" or recover your account for you.
These are almost always scams preying on your urgency. The only legitimate way to recover your account is through X's official support channels.