1.Open the app once and then log out of the game center linked to banned account.
2.Then go to the other iPhone make sure that you haven't used the banned account on that iphone. Just download CSR 2 on the other iPhone and start game and finish all tutorials.
3.Once you done with racing tutorial, link the new account with another apple id(not the same one which is linked to banned account) by making a new one.
4.Now go to settings> Game Center on your phone in which you have banned csr account and log on with the new apple which was made on other iPhone.
5.Open CSR 2 and you will see a message saying ban lifted. As soon as you see that message tap okay button and quickly go back to settings and logout of Game Center account. BOOM now you are unbanned on your unbanned on your CSR2 account and you will be able to play online.
WARNING: Now you should login to any Game Center account because if you login in with banned account you will get banned message again or if you login to new account it will start loading level 1 account