You will in all probability need to contact Customer Service and speak to one of the representatives to retrieve this information. It will also be helpful to provide as much information as possible as to when you purchased the software, invoice number, etc.
Go to your account page and click the Forgot email address link.
If that's no help then call them, it's a toll-free call.
Customer Service 1-866-622-3911 6am -6pm PDT Press 5 for Account enquiries.
I've noticed that the online chat is offline so don't try that plus phoning is far easier.