As stated on this page, you have to call 1023 between 2 and 4 weeks before moving to give SFR informations about your new home (address, when you'll be moving, new address phone number), so that you can transfer your Internet offer.
I suggest you reach someone by calling 1023 to see what can be done. Be sure to speak french or to have someone who can do it for you.
Have a nice day.
Thomas, Community Manager à votre écoute
Un mot inconnu ? Rendez-vous sur le Lexique de la Communauté SFR !