You're best bet is to submit an ESO support ticket (if you still can) telling ZOS the account maybe compromised, they can then block/suspend it until it's back in your hands (this stops someone messing with your stuff).
You also need to contact Steam and your old Email provider ASAP to try and start the process of locking them out and recovering the accounts.
If you're able you should also start changing passwords for anything else you've used that password on.