Cant unlock bootloader after 7.0 update

[leaderred]

Hi, i have following problem.

I have installed MIUI EU Rom with Android 5.1.1 with Root and unlocked bootloader.
With Titanium Backup i freeze some Mi Apps, like Mi Account

After that i installed newest Update of MIUI EU Rom with Android 7 with Update function, not with twrp. i lost root and my bootloader is locked.
I received the unlock code from xiaomi and want to unlock bootloader. But for that i have to link my device with my xiaomi account.

The problem is, that i cant unfreeze the mi account app, because i lost root

I found no other way, to unlock my device or get root.
Downgrade don't work, factory reset don't work, reboot to recovery don't work
Device shutdown and must be started manually every time. After Reboot it stays on current rom without any changes

Any idea how to unfreeze or reinstall my mi account app, link my device to xiaomi account or to unlock my device?

 

[Kéno40]

You have to erase all the data and reinstall the last build.
Then reconnect to your Miui account.

 

[leaderred]

You have to erase all the data and reinstall the last build.
Then reconnect to your Miui account.

But how can i do that?

I cant access recovery or flash things with fastboot
I cant flash a rom with Updater App. Phone restarts, shutdown und must be restartet manually. Rom not changes
When i try "factory reset" in settings, phone shuts down, same thing. Nothing changed

It seems, like revovery is not working anymore and i cant flash new one because bootloader is locked.

Is there an option to reset data by fastboot?

Does "fastboot erase userdata" work with locked bootloader?
And will it unfreeze "Mi Account", because its a system app, not a user app?

 

[Kéno40]

Mitools via fastboot. You'll have to erase all