Subscription

One way to check is through your vehicle's app. For example, I drive a Buick and use the myBuick app. If I tap my initials in the top right corner and scroll down a little, there's a section called OnStar Plans. 

That shows my current plan, and underneath it says "Are you looking for a new plan? Shop all Plans" (with "Shop all Plans" underlined). If you click that, it opens a page with the different options you can look through. 

Hope this helps!