I have two VOIP call-detail-record files that are at the centre of a billing dispute and I need a clear, defensible comparison of them. The goal is to line up the calls in both files, calculate each side’s duration, and show me only the cases where those durations don’t agree. The final deliverable must be a single CSV file that I can forward to the carriers as evidence. Deliverables • A consolidated CSV that pairs matching calls, shows duration A vs. duration B, and includes both the raw difference and any percentage variance. • Only the calls with unmatched durations should be highlighted or extracted; fully matched records don’t need emphasis. • My two original CDRs returned untouched, plus any script, query, or workbook you build so I can rerun the process on future data. Use any reliable approach you prefer—Python with pandas, Excel Power Query, SQL, or similar—provided the results are precise and the process is repeatable. If you need column mappings or sample rows before starting, just let me know; accuracy is critical for the dispute.