How do i cancel an autopay i set up through turbo tax?

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.

If my return was rejected due to the ongoing PIN issue, is the autopayment feature automatically invalid since I mailed the return with payment?

If your e-file was rejected, no information was transmitted electronically to the IRS.  The IRS will only receive your mailed tax return and mailed payment.