Hi! If you are 100% sure you did all the steps and that is receiving SMS approval, your phone on latest official china dev ROM, usb debugging and OEM unlock turned on in developer options, logged in to your fully activated mi account on your phone, phone in fastboot mode, have the right drivers on your PC, logged in with that same account in Mi flash unlock tool. If you have done all that(and please be sure, check again if you are not sure) and you still have that error saying "Account info is different....." then i have dissapoint you a little bit.
Only thing you can do is wait, possibly next week. I had the same problem with my redmi 3, received SMS for unlock on tueseday, and couldn't unlock my phone untill sunday evening. Regarding time zone, sunday evening in europe is very early morning monday in China.
I asked on en.miui and mods there told me for some users this can happen, and some kind of server information is needed to sync, and therefore we have to wait next week.
You can check every once in a while, maybe you can do it another day, perhaps try with another PC. Maybe it will work for you. For me nothing worked except waiting for next week
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