Q: Apple ID email issues

Hello everyone.

Basically, I recently got iTunes gift card from my aunt. However, the gift card only applies to the Mexican iTunes store and my account was from the US store. Therefore, I decided to create a new account to use that gift card. But before I created the account, I decided to switch the email address from the US account to my personal one (previously it was my dad's). After I ajusted the account, I then proceeded to create the new account and use my dad's email as the Apple ID. However, it strangely said that is was still being used as an Apple ID. I then signed out of every device I owned and tried again only to have the same result. So then I decided to change back the original email on my US account and try create the new one with my personal email. However, it also said that my personal email had also been used as an Apple ID.

Another strange thing that happens is when I log in to my account, I type in the original email as the Apple ID entry, but then my personal email appears as the Apple ID in the account settings.

I would really appreciate if anyone could help me out of this tangled situation because I am frustrated and confused on what to do! Cheers