Cannot change my Apple ID
I have got into a dreadful muddle with my Apple ID. I created a second account on my Mac and used the same email address — a gmail one — as my ID on this new account as on my main account. When I went back to my main account, nothing seemed to work as far as my Apple ID, password and rescue address were concerned, so I changed my ID to my btinternet address. I have a third, college staff, email address, so I changed my rescue address to this one (which I have never used before in this context).
Because btinternet mail is so unreliable, I now wanted to change my ID and primary address back to my gmail one, but I received an error message saying that that address (ID) already exists. So I deleted the second account I had created. But the error message still persists and I cannot change my Apple ID to be the email address I regularly use now, i.e . the gmail one.
1. How can I restore my primary email address and Apple ID to my original gmail one?
2. If I now recreate my second Mac account, what should I do about an Apple ID on that account?
Mac mini, OS X Mountain Lion (10.8.5), iPhone 3G