Tonic.to appears to be the authorized domain registrar. Register.to appears to have been a reseller.
I searched the Internet for any Representative, to no avail.
Thank you, shagie, your link did the trick.
Some of the history of the domain can be read at Domain Names, Tonga and Two Guys Named Eric - https://www.latimes.com/archives/la-xpm-1997-06-09-fi-1560-s...
(and amusing to me the email address of the reporter was @best.com - and I remember that ISP from my days out there too).
Tonic.to appears to be the authorized domain registrar. Register.to appears to have been a reseller.