I received the same email from google altough mine is 28. I assumed that it is because of an apk in beta release is using the 26 , mail states that "in production or testing tracks- so you probably have a apk in beta,alpha or some testing track, I don't think what you did can resolve the issue.
anyone knows how I can remove the apk from beta, I can't move it to production as it is an very old version and I cant delete it.