Closing a French Cell phone account outside of France

Hello, My husband and I recently moved out of France.  We kept our French cell phone services, till settled in and got new ones, I thought there would be an easier option of closing them from outside of France, but I cannot find any information, apart from the usual sending a lettre recommandée.  I was wondering if anyone had experience with closing their French cell phone while outside of France ( we are with Free Mobile )?  Is the lettre recommandée required, and if so how do you send it from outside of France?  And also if that is the way to go, would anyone know if closing two accounts using one letter is acceptable?  Thank you very much!  Any help will be appreciated!