iPhone 6s won't turn on or charge.

After an update some months ago, my iPhone started misbehaving in the way where the battery would drain very quickly and would take a long time to charge. And soon after it started killing itself (just shutting down completely), and even when plugged into the wall it will not charge or turn on. It does flash the Apple logo on and off with no charge screen. I've had it plugged in for 24 hours at a time and still no progress. I have even tried to do a hard reset, and no go. Computer won't even detect it when it's plugged in to iTunes. I no longer have access to the IMEI or MEID number as well, but theoretically that info should be on our service account since it was purchased. Please help!