It's not the countries which require or not require tax verification, but the networks. It's not even a verification, it's a tax form for the IRS, what you need to fill out. As an international publisher you need to fill out a W-8BEN form with any legit network you work for, you can't avoid this. You made a mistake applying as a US publisher, because you won't be able to fill out a W-9 tax form.
You're left with 2 choices:
Ask them to change the country. I'm not sure, if they will be willing to do it, it can be that they will simply disable your account.
Apply for a new account from your real country this time and make sure, that you don't link your new account to your previous one.
I know that you applied as a US pub for easier acceptance, but it defeated the purpose.