Why did you re-install from scratch? Do you still have the shared folder from the old instance? If you copy over the letsencrypt and ssl folders you should be able to use those certificates. Mostly, you’d just rsync over /var/discourse/shared from the other server and rebuild. It should re-use the existing certificates.
If you do have access to those files and it’s an emergency that you want to throw money at, see Fix Your Broken Site – Literate Computing, LLC. I should be at my desk for at least the next hour or so.