I made a ticket and a bug report. I got an answer quickly from Trion : "Unfortunately, this is an issue in which we are unable to provide an immediate fix or workaround for you. Our development team is still in need of information from players, so that they may replicate this issue. The best way to do this is for you to submit a bug report, to explain the issue and how it happened in your own words."
I reply to the ticket saying that I already did the bug repport and that I do understand that they need more information but that I still got the wrong essence for my class and I ask again if I can have the mage essence that is equivalent to the cleric one I got. A few days after I get an answer : "I apologize for any inconvenience this issue has caused, and I can certainly understand how a bug within the game would cause frustration. Unfortunately, this is not something the customer service department is able to address. Thank you for submitting the information directly to our QA and development departments. The Intelligence, Wisdom and Endurance stats seems to be also good for Mages."
I didn't find the right solution from the Internet.