Register.com Customer Service Issues

I am experiencing difficulty logging into Register.com as I have forgotten my password and the street is not recognized. When trying to use the domain name, airportparkingmanchester.net, as an alternative, I was informed it was not registered with Register.com but with Registrar.com. Unfortunately, I lack the original registrant's name and access to their email. Despite not wanting to transfer the domain, I need to point the A record to Heart Internet for hosting. Heart previously hosted the website in [redacted] and [redacted], but due to a hosting package issue, details were lost, causing the current display of a Heart message instead of the business index page. I am struggling to resolve this as many security requirements are missing, and the prior owner seems to have disposed of all login information. Though I understand it may be challenging to assist, any help would be greatly appreciated. Apologies for the lengthy message. Best regards, Sue McDonald.