Read my two posts above your last one.

Make sure you read this link that is embedded in that story. https://www.tax.ny.gov/pdf/guidances/corp/g17_1c.pdf

The consider the locked phone to the part of the plan. Even if there isn't a plan.

I found this on the issue.
...

It might or might not list a free service on the bill.

I wonder if any amount of "free cell service" was provided when the phone was purchased? If so there could be a tax on the value of that service.

I think you need to talk to someone other than the 1st level customer service rep.