First are you 100% sure you only have one MySQL server that both your PHPMyAdmin and WAMP can be connecting to?
If so, the easiest way to resolve this is start from scratch and setup a new MySQL user, a new database, then give that new user access to the database.
You need to connect to MySQL as your root/admin user (or run SQL commands through PHPMyAdmin), and any errors with these commands might shed some light on the issue. You need to run these commands exactly as shown, replacing the strings databasename, username, and password with whatever you want but leaving everything else exactly as shown:
CREATE DATABASE databasename;
CREATE USER 'username'@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON databasename.* TO 'username'@'localhost';
FLUSH PRIVILEGES;
Taken from docs here
If these commands are all run successfully, and there’s no possibility that you have different mysql servers, then afterwards you will definitely have a user username with password password who can access the database databasename. Obviously if you cut and paste anything wrong, or use different values when you setup WordPress, it won’t work 😉
Hope that helps, please reply here if you’re still stuck or if any of these commands give errors.
If you still have problems then sharing how you are viewing your databases, users and permissions will help debug.