How do I recover my RDS?

If you closed your account less than 90 days ago, then you can sign in to your account and file a support case to reopen the account. After 90 days, you can't reopen your closed account or open a new AWS account with the email address associated with your closed AWS account.

For detail https://aws.amazon.com/premiumsupport/knowledge-center/reopen-aws-account/?nc1=h_ls

https://aws.amazon.com/premiumsupport/knowledge-center/reactivate-suspended-account/?nc1=h_ls