Back in October you obtained a separate certificates for addmee.net before you obtained a combined one for addmee.net and www.addmee.net
You renewed the combined certificate ( for addmee.net and www.addmee.net) in December, however the original certificate you got ( just for addmee.net and no longer needed) has not been renewed and is about to expire. You can safely ignore the emails, as you don’t need that certificate any longer.