Ted here from Shopify, thanks for posting your query!
Sometimes when merchants select a plan, Shopify's system will close the store so that it can be manually reviewed by our Risk Department. This only occurs for new accounts created just so we can verify the account for security reasons. As you mentioned you can no longer access the admin as well, I do believe this is the issue but I have emailed you privately so I can help authenticate the account and take a closer look. Please note that if the account is under review with our Risk team, then it can take a few business days for them to complete the review. They will get back to you as soon as possible once it's completed.
For anyone else reading this, please contact our support here for immediate assistance, just click Support > Contact Support in the main menu to get started.