So here's the problem with unlocking my 4c.
The Mi Cloud service was disabled via Titanium Backup app so now, after flashing the buggy 7.2.9 (the one with the battery drain problem), I can't unlock the bootloader (got a permission from xiaomi) due to "couldn't verify the device". From what I read on the internet, I believe this has something to do with the Mi Cloud service being disabled on my device.
And the problem is I can't perform a 'reset' thing to get all services up and running, the phone just reboots and is stuck on Mi logo.
Can't think of any solution in this case.