Being billed for a "Digital Converter"

I realized I have been getting billed for a "Digital Converter" I never ordered and never used. I believe it is for an Xfinity Flex. I called customer service and they said they removed it from my account. When I went to look at my estimated upcoming bill, the charge is still there. I have been billed over $300 over the last 24 months for this, so I requested a credit. The customer service person said they could not credit for past month, so I requested the ticket be escalated. The agent told me I would receive an email within one week from an escalation person. It has now been two weeks and nothing ever came.

I need this addressed. Please assist.