How to access iCloud if my mail service provider doesn't exist anymore?

I need urgent help from this community. The issue arose when I upgraded my Mac to Maverick. I have lost the connection to iCloud (and all my data) because iCloud asks me to enter the password of a former e-mail address that was discontinued by the sevice provider years ago. When that happened, I changed this mail for another one in the same iTunes account and I have bought many apps and music from then. How can skip this request and get the access back to iCloud? Thanks!!