Google Play Music Direct Carrier Billing

Anyone else using 2Degrees to pay for Google Play Music subscription?

Been using it since the family subscription was made available here in NZ (and 2D carrier billing), and has worked well. Last month, however, I got an email from Google that said payment was declined. In trying to sort this out with 2Degrees via FB Messenger, which is the only place where I got a useful response from (call and email got nowhere), I have:

Removed 2Degrees as a payment option and re-added it

Changed my SIM card

Re-added 2Degrees as a payment option

And I am still unable to select 2Degrees as a payment option for Play Music. Funny enough, it's acceptable for Play Store purchases, but I can't even select it for Play Music.

What infuriates me is that this has been working for some time. All of a sudden, it doesn't and no one seems to know why.