Security code for the radio for my Renault Megane -?

After having a problem with my electrics the AA reset them and the radio now does not work and is asking for a securitycode to be inputted? how do I get this as did not buy from a renault dealer just a small garage?. do I need to call Renualt with reg no or is there a code I can put in?
Hoping you can help.
Sam