I have just been able to pay my bill! I emailed them AGAIN and got a response back. I clicked on the link for the ticket and it took me to a new portal!
Client Area - Gamers Services I then logged in using my normal details and bingo I could pay!
I have a $5 a month and was on mint/gmasterpanel
In the email it also gave me a new filelinked in number, which I just logged into.
The GMX app is gone and obviously not working but there are guides to using and downloading other apps to run the service.
ENJOY!