Double Billing of Cell Phone Insurance

I have been trying to resolve an amount that I have been billed over a period of time since November 2021. A credit was passed on 02 December 2022 but this is way short of what I was incorrectly billed. I have requested a detail report of what they credited and to date have still not received it. This has been an on going problem since November 2022. You are unable to speak directly to the billing department and despite submitting a detailed summary of the incorrect billing, you get no where.