What is PRO BTP certificat d’adhesion and do I have to do anything?

I have had me auto entrepreneur business (handyman type work) set up since January this year. I received a letter from PROBTP a month or so ago which I ignored thinking it was junk mail. First letter enclosed a form to complete Demand Adhesion. Anyway they have now sent me another letter enclosing an actual certificat d’adhesion, L’adhesion de votre entreprise aux regimes Arrco et Agrirc a ete enregistree par les institutions de retraite complementaire suivantes:.. and the covering letter seems to state that I signed up with them even though I have never sent anything to ProBTP. This covering second letter states:

Nous avons procede pour vous aux formalites d’adhesion conventionnelle de votre entreprise aux regimes de prevoyance et de retraite geres par PRO BTP, votre groupe de protection sociale, ainsi qu’a la formation professionelle, pour laquelle PRO BTP se fait l’intermediaire. Vous trouverez dans ce courrier l’ensemble de vos certificats, a conserver. Nous vous joignons aussi un formulaire de declaration d’affiliation pour declarer toute embauche, depart ou changement de categories professionnelle d’un salarie. Bien entendu, vous pouvez effectuer ces demarches sur notre site internet.

There is another form enclosed with the letter and certificates asking for a Declaration D’affilation ou de radiation de vos salaries. If I don’t have any employees (I’m auto entrepreneur so wouldn’t) can I just ignore this form or should I send it back stating that I don’t have any employees? Do I have to do anything else with these certicates d’adhesion or do I just file them for the future?