Why do you think there is a third party processing your tax payment? That would only happen if you selected to pay by credit card. (If you select pay by bank debit, that information is passed directly to the IRS and the IRS makes the debit.)
As far as I know, if you select pay by credit card, that information is passed to the credit card processor as soon as your e-filed return is accepted and there is no way to stop it after that.
