Direct Carrier Billing

Okay, it's a lengthy response, but it contains more information that I've ever come across. LOL. 

If your issue hasn't been resolved, contact the customer support again, by phone. Once connected, politely tell the rep you would like to speak to a supervisor. The rep may try to discourage the transfer and ask you to allow them to give it a shot. If you prefer just to talk to a supervisor, just explain that the issue has been ongoing for too long and needs a supervisors assistance.  If the CS supervisor is unable to assist, ask them to transfer you to the billing department. (Reason I think billing dep could help is because the only info I found on the Tmobile website for carrier billing (which is EXTREMELY short and vague) was in the billing FAQ, under the Apps and subscriptions section. 

Here's what I know from my experience as a current T-mobile customer and occasional direct carrier billing user:

ANDRIOD:

-Only the Google Play APP allowed the use of Tmobiles carrier billing. 
-The Play app allows carrier billing to be used as a payment method for:

*Purchases of paid apps

*If applicable, apps with subscriptions (ie: monthly/yearly fees for accessing all/some tools/features

*In some apps, in-app purchases. (ie: removal of ads) NOTE: Certain types of in-app purchases are not available for this payment method, and an app may offer both compatible and non-compatable options. The only way to know which is compatible is to select preferred in-app purchase and proceed to the payment option screen. If you see your mobile number, that in-app purchase is compatible.  The popular gaming app Roblox offers optional in-app purchases for their special currency, Roblux. Prices range anywhere from $0.99 to $199.99.

IOS

Direct Carrier billing is only available customers in select regions. US customers with IOS devices are unable to use direct carrier billing at this time. 

Purchases made with carrier billing may not exceed  a total amount of $80/billing cycle. No exceptions are made.