Unresolved: How Can I File a Formal Complaint and Get an Executive Review for a Systemic 11-Month Billing Error?

My internal resolution attempts have failed, generating multiple tickets (ECM0018136409 and ECM0018146836). How can I officially escalate this to a team that has the authority to implement a full resolution?

This issue includes: <11-Month Billing Error: Uncorrected recurring charges for Inactive Voice Modem equipment, which has continued on my bill since January 2025, totaling approximately $330.00} that has never been credited.Failed Credit: An agent promised a $130.00$ credit to address the error, but this adjustment was never applied.  Systemic Service Failure: I have experienced repeated disconnections during live chat, excessive wait times, agents telling me the fault was mine for not checking "page 3" of the bill, and the consistent use of a "system limitation" excuse to avoid issuing the necessary full credit.Redundant Charges: I also need a review of the redundant  charges. I require assistance from a representative with the executive authority to apply the full credit and restructure my service. Please advise on the next steps to move this into a private, owned resolution.