As mentioned in the topic, this problem came up when I decided to suspend the patron status to make other in-game purchases (note: I don’t have Steam account)
The system no longer recognized my credit card, and when I tryed the “change payment method” option in the aurum purchase confirmation checkbox, the site page opened in the browser but did not recognize the user.
I contacted the support but as usual I have not received any response.
I later discovered that in order for the site to recognize the user (and therefore register a new payment method, or reactivate the previous one) it is necessary to enter the game character selection page and click on the Account button . Once that page has been opened in the browser, the site will be able to recognize the user when he uses the appropriate link in the aforementioned checkbox.
I hope this will help those who will experience the same problem.