Hi Kate,
The free site retention policy is there to ensure we can continue to provide free and low cost Moodle hosting options for all. We do send an email to the admin of your account well before the removal. If your site is not going to be used for a period of time, you can choose to upgrade to one of the plans where the policy does not apply.
I can see how this is frustrating for you when you lose your site. Maybe the email got stuck in a spam folder. If you would like to continue with MoodleCloud, email support@moodlecloud.com with your site details and we'll see what we can do with your site.
Thanks
Chris