Falsely Accused Of Tethering!

I have been a perfect customer for years, and I follow AT&T's rules. I know what tethering is, and I have absolutely never done it.

Today, I received a letter from AT&T accusing me of tethering and threatening to take away my data plan. I called the number on the paper, and first talked to a rep - it sounded like she said her named was Donna.

She asked me over and over if I had tethered, rephrasing the question - did I use a tethering app (no), did I try Googling the names of my apps or maybe read the app descriptions more carefully (how ridiculous), did I use Pandora with my car (I don't know what that has to do with tethering, but I have never used Pandora and I have never owned a car).

I asked for a supervisor, who did not provide his name. The supervisor said they would investigate. I do hope they find their mistake, but realistically speaking, I presume they will either just never call back or continue to falsely accuse me.

I asked for details about what caused the warning, and they could not provide any other than repeating the original accusation. They also assured me that the fact that I installed iOS 8 earlier today would be sufficient to prevent any further problems (which doesn't make any sense, but whatever).

Once again, I have never used any form of tethering. I have never downloaded any app with tethering ability. I have never had "the flashlight app." I have never jailbroken my phone. I do not use excessive bandwidth, and I have never gotten any warnings on this account for excessive data usage. I understand that a "first warning" does not automatically cause me to lose my plan, but being falsely accused is unacceptable.

[edited for privacy-please do not post personal or unique information such as but not limited to full names, employee ID numbers, email addresses, phone numbers, account numbers, etc.]