In AU.

Tried MasterCard
Tried Visa (This one has worked with another friend's account)
Bank says everything's fine
Even though I'm set to Australia/Europe & Other Regions, I tried Euro VPN but no luck

Spoke to chat and if I cut out all the extra stuff, here's the relevant info I was advised:

As far as we are aware it's not an actual problem with our systems(it's more likely that all legacy/v1.0 players have now had all their free game time expire so it's why it seems there are so many at once)
...before we escalate this for further investigation we have to ask that you contact your bank to make sure that no payments from SQUARE ENIX have been blocked for whatever reason(it's just something that we need to try) and to make sure that all the payment details are correct. Also to avoid any payment issues you can purchase Game Time cards to add to your account...
...there isn't anything else you can do I'm afraid. If it doesn't work in 24 hours please contact us again and we will escalate your details to our head office for investigation. After that I can't say what will happen sadly
I believe the guy to a degree and have a feeling the issue could be with GlobalCollect's relationship with my bank, though there's been no issues with other friend's with the same bank.