Hello,
Welcome to Xbox Community Forum. Thank you for sharing your concern with us today and we hope that all is well.
We understand that you wanted to log into Minecraft website however you get an error message upon signing in. Let us check on this together and sort this out in timely manner.
Based on your description, you may be having issues with your account or browser, or you currently do not have any linked account to Mojang that is why you are getting an error message. You may try to perform troubleshooting or else contact Mojang to help you with your account issue.
Please see first if you can access this link: Microsoft account site - Microsoft account | Home
Can you access this website using a different browser?
Do you mind signing into Xbox website: https://account.xbox.com/
You may try InPrivate Window of your browser, other browser, different device/s or connect to different network.
Please see if you encounter issues signing in to your account.
If yes, you may still have Mojang account, or else your Minecraft game is associate to a different account.
Let us know the result and we will get back to you as soon as we can. We may recommend further troubleshooting steps once we have received your answers to the above questions.
Sincerely,
Kathy A.
Xbox Forum Moderator
Microsoft Community