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This question has nothing to do with MV
Support needs some time to respond to tickets - up to three business days (weekends don't count). But sometimes tickets get lost - when did you place the ticket?
That said, there have been rare cases of problems with credit cards on the shop. To my knowledge they always happened because of a security measure in the card company: Payments to Degica go to japan, and some companies require specific authorisation for international transfers. That means you need to call the card company whenever you want to make a payment to clear it specifically.
However, some of the people with card problems solved those by going through paypal instead, having the card entered into their paypal account and using that to pay, so I can't tell if it was always a card company problem or something else. PayPal has always worked, even through a card as payment method at paypal.
You can also try to get the Manga Maker through Steam directly, those have different payment methods.
