Thanks for your comment 

I am in contact with our account manager and she says that they can’t give a backup when subscription is inactive !! Is that true ?

and how many weeks Odoo keeps customers database in their server ? 

our ex account manager sent me email before saying that they keep it for 5-6 months and now the new account manager says they keep it for only 1 months !! What‘s the true story ?

You can take a backup any time you like.

If your subscription has ended and you no longer have access, open a ticket with Odoo Support as databases are still available to them for a few weeks afterwards. They can provide you with a backup.

https://odoo.com/help