If your Xiaomi Phone got locked out due to forgotten Mi Account. You may request to have your Xiaomi Phone be unlocked.
I strongly suggest to email or chat all the information to Xiaomi support (Depending on your location, refer to this link http://www.mi.com/en/support/contact/) and if your country or region does not have a direct support. You can email it at email@example.com or firstname.lastname@example.org
Make sure to complete all the details specially the Proof of Purchased or else your request will be declined by the Xiaomi Technical Team who is handling the request.
Once all information was verified, request will be processed within the next 24 to 48 hours (Estimation depending on the numbers of request per day)
Have patience and you will get the sweet result.
Any question? Feel free to comment and I will try my best to help.
From your friendly Xiaomi user,