How can I cancel Onstar Guardian when they have no record of my account?

[VH]

I signed up for a first month free trial of Onstar Guardian on Oct 25th and two days later I received a notification from the app saying, "Your OnStar Guardian subscription has expired. Your services have been deactivated, and you and your group members have been signed out of the app." I don't know what happened but I assumed my subscription was canceled until a few days ago when my card was charged $16.20 by Onstar. I called an Onstar advisor to inquire about this and he searched my name, phone number, and email and found no account. How can I cancel Onstar Guardian when there's no record of me having an account? Is it possible to get a refund for this charge since my subscription "expired" several weeks ago?

[Advisor_Helen]

We greatly appreciate you bringing this error message to our attention. We would like to take a further look into things regarding your Guardian services and assist in any way that we can. If you have any continued trouble with your account, kindly email socialmedia@gm.com with ATTN: OnStar Community/VH in the subject headline. This will allow us to locate your Community post and further investigate.