Did you setup Twilio keys before it (Studio->Settings->Twlion area). If not then UNA can't send your SMS. You need to run this MySQL query:
UPDATE `sys_options` SET `value`='' WHERE `name`='sys_account_activation_2fa_enable';
Then clear the content of the folder "cache" (but don't touch .htaccess file there). After this steps, you will restore the situation before enabled 2FA option.