Email upgraded to Onstar One at no additional cost

I received an email from Onstar that I got a complimentary upgrade to Onstar One for no additional cost to me. Then I got ao $20 additional charge added to my card. I called OnStar, and they said that the package I had was discontinued, so they bumped me to OnStar One.  The email did not say that my package had been discontinued; it just said that, as a Loyal Onstar customer, I am getting an upgrade at no additional charge. The lady couldn't explain why I got the email; all she could do was offer me another package. So I did get another package, which means I lost some of what I was getting before, which is fine, but I want to know why I received the email that I wasn't going to get charged extra, and then I was charged.  I just want to know why i was told there would be no charge and then i got charged!!! I am very frustrated!!!