You currently have the CC Photography Plan and there isn't an upgrade option to move to Illustrator single app. You would need to contact support for cancellation assistance. The cancellation fee may not apply as you are signing up for another plan.
Ok but how can I contact support : is there only phone contact ?
and what about the fake help webpage ?
and I hesitate to buy Illustrator face to the lack of reactivity of French Adobe (Facebook experience) ....
Phone and chat support is available for your subscription product.
I'm not sure what you mean by the fake help webpage? There isn't an option to upgrade from the plan you have currently so our support team will assist you.
Here's the link for the French support page - Contacter l’assistance clientele
Select Creative Cloud as the product
What you need help with - select Abonnement, compte, paiement
Then select - annulation de votre abonnement
Click the blue bar - "Encore besoin d'aide? Contactez-nous"
You will then get the phone/chat options