Q:

Problems with user's privileges, wordpress, phpmyadmin, my host provider and I hope that's all

So I've been trying to install a new wordpress site beside an already working site. I want to have 2 different databases, so i created a new one, and I didn't go very far from that. I get the message "Can’t select database" in /wp-admin/, and in the sql_error there is : "Access denied for user 'user'@'host' to database 'database'"

After creating the database, and went to phpmyadmin to create a new user and his privileges, but there's no privileges tab in phpmyadmin. I did empty cookies and all, but with no effect.
My host provider provides "mysql databases" tool. There is a drop list to make associations between schemas and users, so i did it, but there is no way to control that it's really taken into account
I installed chive, but i can't find the privileges tab neither
with sql queries, in phpmyadmin, i can't add any privileges, i get a "access denied to my_root_user on my_schema"
It's the same errors when i try with an old user on the new schema.

Does somebody have a clue on what to try next ? If that comes from my provider configuration, how can i get the proof ?

A:

Ok, meanwhile I've send a mail to the support. 
They told me they deactivated the user management in phpmyadmin and that I have to go through the cpanel.
That, I already tried. 
But he told me that if I have difficulties to add the privileges, I have to deselect one of the checkbox (the "trigger" grant), without using the "all privileges" checkbox.....
So either according the trigger privileges to a user in wordpress breaks it, or my provider have shitty management tools.

