Here is what the issue is from my perspective.
Back in July we upgraded a phone to ATT Next. We were aware of new billing for that device, but it was not disclosed that it was going to change the access fee for the other three devices on the account at the time to $40/month (from $30/month).
At the time I had been traveling quite a bit for work and I had been going over on my data plan. Rather than spot the discrepancy right away I assumed the higher bills were me going over on my data.
Fast forward a couple of months (to September) and we add two additional devices to the plan. At the store we asked to do a plan that kept us at $300 (no more) due to budgetary reasons. We were told that was the case. So we had six devices and we upgraded to a 20Gb/month plan.
The first month the bill was higher than I anticipated so I contacted customer service via the online chat. The support rep shared with me that the first month was getting all of the one-time fees (minus the taxes that were paid at the AT&T store wh