Consider sending an email to merchant support, they can look into the account.
Contact page link: https://help.shopify.com/en/questions#/contact/
If the link keeps redirecting to the home page, try opening the link in Chrome Incognito mode.
I would suggest clearing your browser's cookies and cache, and then try to access the admin from your store's custom .myshopify.com URL. This would look like the following format: yourstorename.myshopify.com/admin. From there, you can then enter the corresponding email address and password that is used to login to your store.
For further context, is your customer-facing website available and loads ok? If so, the issues here might lie within your browser, or an incorrect email address or .myshopify.com URL was perhaps entered during the login process.