Your Courtesy Rating is automatically calculated in-game, only depending on your connection and the way your matches end, and these reasons are why we can't change it for you.
So, despite the fact that your Internet connection might be very powerful, some elements (programs taking up resources on your line, router settings, anti-virus etc...) can weaken it or make it unstable, causing disconnections and lowering your Courtesy Rating. To avoid these kind of disturbances, we recommend that you check your Internet connection and any settings related to it. Once you have done this, you will be able to play matches, complete matches without disconnections and regain your Courtesy Rating.
We also want to assure you that we are aware of certain users playing unfairly online in PES, however, the Courtesy Rating system is already an action against troublemakers and their disconnections will not affect your Courtesy Rating in any way.
You are the only one who can regain your Courtesy Rating and after the above changes you will get your A rating back in no time and you may even reach the AA or AAA rating!
To check the status of the server in real time, you can visit the web page http://www.konami.jp/we/online