We hope you don't mind us replying in English. It sounds like you're not able to take part of the Premium for Family plan.
If you see that you're on the Free service, we suggest that you make sure you don't have another account connected to the plan. You can check this by asking the owner if they can see you in their list of family members on their account page. You can also check out this help article to look for other accounts.
If you're not present on the list of family members, ask the owner to send you a new invite, and see if you can join.