I think this article will answer some of your questions - https://www.adp.com/resources/articles-and-insights/articles/w/what-is-calsavers.aspx

It looks like your previous employer may have enrolled you. Check your credit reports to see if you are currently employed anywhere or if there's anything strange. If there is, then you may be a victim of identity theft. If there isn't, then you just got notice of your previous employer enrolling in it.