FormAssembly plugin disappeared from site, unable to download again

Our Company have been using the WP-FormAssembly plugin to embed forms on our website.
Recently the plugin just disappeared from our WordPress site (presumably following a WP upgrade). We cannot find the plugin under installed or uninstalled plugins. Also when we try to download the plugin again it does not give us that option. Please assist as it provides critical functionality to our website. Our forms are no longer available on our website due to not having the plugin installed.

Please assist.