I understand you tried to add a different credit card to pay for your Shopify bill, but your store suddenly became inactive after doing so.
That is certainly not an ideal situation, so I can understand why you would be eager to get this resolved and get back to your store.
I would love to be able to find out the exact reason why this happened and help you fix it, however here on the Shopify Community we do not have access to account specific information.
If you haven't received any emails from us in relation to this issue, then I would recommend reaching out to our support team via this help centre link. There, we can authenticate you as the Account Owner and take a closer look at why this might have happened.
Please do let me know if you are having any issues contacting us.
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