Anything you do will be shutting the stable door after the horse has bolted.
At some point your account has been hacked and your contact list stolen, it can't be 'unstolen'.
If a burglar cam to your house and stole your paper address book, there would be nothing you could do to prevent the burglar using the addresses.
Change your password to prevent re-occurrence and inform your contacts to ignore spam emails purporting to come from you.
