Had apple support help me with this:
On your computer, go to appleid.apple.com, and sign in using your current apple ID.
Once signed in, change the primary email address to the one your phone is asking you for (ie. your old apple ID), enter the password you want to use for iCloud.
Go to your iPhone --> Settings --> iCloud. Now you can enter the password for the old apple ID. Delete the account.
Go back to your laptop, change the primary email address back to the current one. Now you'll be able to enter your current apple ID and password on your device -- should be good as new!