Hello mauli,
You can absolutely use the social security number that has been given to you in the past, it will remain the same (if it was a permanent one). But you need to reapply to french social security system.
I invite you to contact caisse primaire d'assurance maladie (CPAM) calling 3646 or the English advice line 09.74.75.36.46 to know which documents you need to send according to your situation.
Once your file will be proceed, it will reactivate your number and then, you will be able to access the ameli account.
Have a nice day
