Regarding usernames, epiz_ usernames are common with old accounts (when epizy.com was still available as a domain option). New accounts usually start with if0_, just like in this case.
This also isn’t an issue here, while usually a common mistake, in this code = is meant to be used, as the value of mysqli_connect is assigned to the variable $con, the value of which is then checked (if !$con).
I’d assume you don’t need to do the change in phpMyAdmin but in the file manager/via FTP, on your files (unless the database host value is also stored there).
While this is informal, but it happens to me when I try to access the phpMyAdmin directly (from address bar) instead of clicking the button in the panel. You should try clicking this one here again:
Be patient friend. Calm down. If it still doesn’t work, there is nothing we can do. That would be a technical issue and would get addressed by InfinityFree team eventually. Whether they would fix it or not is a different topic.
If they don’t, you can use other services.
Also stop resetting passwords or cookies, that is useless because this isn’t on your side.
I am sure its because they are upgrading infrastructure, so just sit this one out… for now.