Unauthorized Line/Phone added onto our family plan.
We currently have a family plan under att and recently discovered that there was an unknown/unauthorized line on to the plan. We only discovered this after one of my brothers broke his phone and asked to check if we had any insurance on the phone via att. The primary account holder is my mother with zero to little knowledge of English. This unauthorized line had been on our account at least from Feb. 2018, and no one within the family has been using this since the data, text, and call has been at 0% usage as far back as i could check. I also noticed that this line was an iPhone 8 that has been financed but had an "NEXT iPhone 2018 New Year Promo _ of 8" added onto it which covered the installment cost of this unknown phone, and my mother had just been paying for the extra line. She has her payment on automatic payments and only thought it was the price it was due to her calling internationally often for work and family.
Has anyone had this happen to them and know the course of actions to take?
I had called att to remove the line and was successful after being put on hold for 2 hours, but had gotten the run around when I had asked them if there was a way to pinpoint which store added this line onto our account, and if there was a way to find the serial number or imei of this phone.