I think we talk at cross purposes.
I was writing about the validity of the SIM card itself, while you obviously mean the validity of credit, which is shorter depending on the amount of recharge:
5€ - 1 week
10€ - 15 days
15€ - 1 month
25€ (+ 5€ bonus) 2 months
35€ (+ 10€ bonus) 3 months
50€ (+ 15€ bonus) 4 months
75€ (+ 25€ bonus) 4 months
100€ (+ 50€ bonus) 5 months
source:
http://sites.orange.fr/ge/content/pd..._mobicarte.pdf, page 3