I returned my 2011 Volt back in December of 2013. Just the other day I was using the Onstar app and the car was back on my account. I called Onstar to have them remove it again. I think this is a security issue as I could unlock the car, good think you can't locate 2011 Onstar vehicles.
My guess is that the car was recently sold and someone re-activated the car and it went into the wrong account.
My guess is that the car was recently sold and someone re-activated the car and it went into the wrong account.