How do I cancel my scheduled federal tax payment?

You are asking too late.---You say it was scheduled for today.  You should have cancelled it last week.

TO CANCEL A TAX PAYMENT YOU SCHEDULED

If your return was accepted, you cannot change your payment method  or payment date.  The only thing you can do is cancel the payment and then pay by a different method on your own.

• Call IRS e-file Payment Services 24/7 at 1-888-353-4537 to ask about or cancel your payment, but please wait 7 to 10 days after your return was accepted before calling.
• Cancellation requests must be received no later than 11:59 p.m. ET two business days prior to the scheduled payment date.