Sorry to hear that. Those issues are typically the result of a defective battery, a battery that is failing. It's probably displaying the wrong percentage all the time. It could be faulty software also, backing up all of your personal data to a safe location off the phone and doing a factory reset will help determine if the issue is with faulty software or a faulty battery. If it keeps shutting off after a factory reset then it's probably time for a new battery (or a new phone depending on how much a battery will cost). Hope that helps.