Apparently, AT&T and Google are in the process of breaking up. On its "Accepted payment methods on Google Play" support page, Big G announced that, soon, AT&T billing will no longer be supported as a payment method (via Android Police).
From this month, new subscribers and users who don't currently use a carrier billing for Play Store purchases won't be able to use their AT&T monthly payment to pay for digital content on Google's app store. Those who are currently using this method can continue to do so, but only until September.
Currently, there is no information on why that decision has been made. Both Google and the carrier remain silent on the matter. However, AT&T isn't the only operator to be dropped from the Play Store's payment system.
At the beginning of the year, Verizon customers also had to deal with the news that they would no longer be able to use their subscription plan to make Play Store purchases. Back then, in a statement, the carrier said that the withdrawal from the Play Store's payment methods was a "business decision."
So, with Verizon gone and AT&T on its way out, the only mobile carrier billing supported by the Google Play Store are Boost Mobile, Sprint, T-Mobile, and US Cellular. AT&T and Verizon customers still have the options to use credit and debit cards, as well as PayPal and Google Pay.
To change your payment method, open the Google Play Store app and tap on your profile icon located at the top right corner. Then choose "Payments & Subscriptions" and tap on "Payment Methods." After that, select "Edit Payment Method," tap "Edit" on the option you want to change, and then choose another way of paying. Then, tap on "Update" to save the change and finish the process.