I have the identical issue. After calling apple support 3 times and 3 times finding out that neither the operator, nor their supervisor can get with apple developer support and has no email nor phone number - I really don't know what to do. Did anyone solve this?

I have the same isse: "This email address isn’t valid. To update your email address, visit account.apple.com." And I cannot reach developer support in any way now. General Apple support tells me they cannot help me neither as they themselves have no access to developer support. Did you get this resolved?