I can't get an old Email address off my apple ID

I can't get an old Email address off my apple ID. The old address is unavailable and I can't use it as I don't have the password. My current ID is alright. I have reset my phone twice but when I go to ICloud it reloads the old address on features of my phone and I can't use them. I have reset up my phone as a new one and that's fine but I am afraid to Sync or restore for fear of reinstalling the old ID. What should I do ?