If you still have the order number they can use the automated password reminder system or if not then, an email must be sent from the administrative email address on the account to admin@tremhost.com. Concluding the original domain name it was purchased for, or the original order number.
Related posts:
I haven’t received my Domain Control Validation email (DCV) yet. What should I do?
If I buy a Domain Validated (DV) SSL Certificate, which document(s) do I need to provide?
What is the difference between Wildcard and SAN/Multi-Domain functionality?
Why does the website say the name on the security certificate does not match the name of the site?
