If i press PAY NOW (which is instantly (( I know it because kaspersky and many other use Digital River aswell))) it just sends me back to the login and i have to re-do the process over and over again without any informations like: Successfully payed etc..
First, you were already answered to by email so, please, don't post the same question twice by email and forum, because all emails ARE of course being answered, and email is clearly the best place for purchase-related questions.
In any case, when you are on the PayPal page which contains the Pay Now button, you are inside the PayPal site, and we don't have any control on it, everything (right or wrong) that happens there, it's entirely under PayPal control and if something doesn't work correctly, it's a PayPal problem, or a problem of your system/browser interacting with the PayPal website.
This means you should be able to fix your problem asking PayPal support first.
There might be also a chance the problem it's not PayPal by itself, but an interaction between PayPal and Esellerate and, again, it's nothing we can control so, if PayPal can't explain the problem, you should then ask to Esellerate support instead, at support@esellerate.net