ok, nice, successfully got my account number from that second link you found.
Unfortunately still getting the same error at https://my.chevrolet.com/api/vehicleProfile/<YOUR VIN>/<YOUR MYCHEVY ACCOUNT NUMBER>/evstats/false
{"messages":["Unknown error"],"serverErrorMsgs":["Unknown error"],"data":"SERVER ERROR"}
Do you by chance pay for OnStar? just curious if that's a differentiating factor...