Can't update apps but can download them; doesn't accept (valid) virtual CC. What to do?

Question

I can download new apps but can't update the existing ones. What happens when I press "Update all" is the following:
App Store asks me for the password, it recognizes it as valid, the icon of the apps change from "Update" to that circle that should eventually fill up, but then all icons convert back to "Update".
I don't have a payment method associated with my account (I used to have one). When I try updating my account with the information of a (valid) virtual CC, it rejects the card even though virtual CCs have worked perfectly well before.
I have this problem both with the iOS App Store and the Mac App Store.

Answer 1

Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
Select
          /var/log ▹ appstore.log
from the hierarchical list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar.
Each message in the log begins with the date and time when it was entered. Select the messages from the last installation or update attempt, starting from the time when you initiated it. If you're not sure when that was, click the Clear Display button in the toolbar of the Console window and then try the installation again.
Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message (command-V).
If there are runs of repeated messages, post only one example of each. Don’t post many repetitions of the same message.
☞ The log contains a vast amount of information, almost all of it useless for solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
☞ Some private information, such as your name, may appear in the log. Anonymize before posting.