Removal of $529 equipment fee

I've called twice and both times I was told the $529 equipment fee that is currently on my bill would be removed. The fee is for a phone that didn't work properly and was covered under warranty and insurance. We paid the $99 deductible and returned it.

What do we need to do to confirm the charge is removed from our balance due? Apparently, calling, waiting on hold for more than an hour, then being told the representative "promises" it will be removed doesn't work.