Thanks for asking question. This is seems strange. App Service Managed certificates is created on your already created App Service which is under your selected resource group. You need to select the custom domain to create a free certificate for and select Create. You can create only one certificate for each supported custom domain. When the operation completes, you see the certificate in the Private Key Certificates list.
Could you confirm if resource group was deleted successfully? Also, if you have bind your certificate to a custom domain of DesignClub resource group?
As, Its mentioned in the document that "You can't move a free App Service managed certificate. "
Let us know.