I used to pay my T-Mobile plan with ACH from the T-Mobile site, but that is not an option. I can only pay with CC. What you’re describing sounds like a rate increase.
"T-Mobile: FINAL REMINDER of Action Needed by 08/06/2023. We’re changing the payment methods that qualify for AutoPay discounts. To continue receiving your $15.00 AutoPay discount, you must update your payment method to a debit card or a bank account. To keep your discount, please visit t-mo.co/AutoPay25 to change your payment method by 08/06/2023."