I have found his post here:
http://forum.gsmhosting.com/vbb/f35/.../#post13374822
He told me he is selling solution for unlocking all xiaomi accounts permanently (account won't come back after connecting to wifi).
I pay him 100$ by paypal, after trying to remove accounts from Redmi 5 plus and Mi8, both phones got locked again after connecting to wifi, he tried many things via teamviewer and he couldn't remove accounts permanently, so i asked him to refund my money, he told me that my phones are blacklisted that's why he can't unlock them (while before he never told me that) and he won't refund my money.
He didn't test his solution and he is selling it telling it can unlock all accounts without relock after connecting to wifi.
Here is history of whatsapp :