One.com - Super terrific experiments to manage the domains

I am so sorry to hear of your difficulties. It must be very worrying and frustrating.

I have never used the company, or actually even knew of their existence before you tagged me, so I don't have anything specific to recommend.

I looked to see if the company had a representative here on NamePros, but unless under a different name, could not find one.
https://www.namepros.com/members/?key=representatives

I also went to company page to see if they were on social media in a way to provide an alternative means of contact, but don't see one.

They have been in business for 20 years I see.

I wondered if they were a reseller or an ICANN accredited registrar, since if a reseller you would have options for resolution through the primary registrar. But they are ICANN accredited registrar 1462.
https://www.icann.org/en/accredited-registrars

You have sort of already done this, but I would restate to them what you have that you have provided everything that is available to you, and ask them what alternatives exist. Do you know personally another One customer who might vouch for your identity, for example?

I take it this has nothing specific to do with the security certificate, but rather they won't let you do anything with the domain because they have, for whatever reason, become suspicious if you are the true owner?

I would ask to have your situation escalated to a manager.

If after trying again for resolution at One, you do have the option of submitted a general registrar complaint through ICANN, but that would probably be a very slow process.
https://icannportal.force.com/compliance/s/generic-registrar

I hope you get resolution without much more hassle.

Sincerely,

Bob