I have the same issue. Called their customer service and they said it was a defect in the charging system. They are sending a upgrade kit for free, but when it's installed you can't charge the battery using the rear port anymore. No big deal. I'll report back when the fix is complete. 5-7 days until it gets here.

Do your front wheels spin when you spin them if not try loosening the nuts a little, if that works or even if it don't try upping the voltage of the battery don't go to high cause you will kill the motors but they will work fine doubled