Put the disagreement into plain words
Ask each party for its report, the exact condition it found, what was tested, and its instructions about use. A utility leak investigation and an appliance combustion or heat-exchanger evaluation do not necessarily have the same scope. Ask the utility what its clearance covers. Ask the HVAC company which specific furnace finding remains unsafe.
For example, “no gas leak found in the areas checked” and “appliance needs a model-specific safety repair” can both be true. That is an explanation of how scopes can differ, not a finding about your furnace.
Carrier identifies gas valves and heat exchangers as components that need qualified service. An opinion about those components should come with an explanation of the applicable equipment checks. Carrier furnace repair guidance.
What to request next
Share both reports with a qualified service evaluator familiar with the model. Ask that person to identify the conflict explicitly, use the manufacturer's applicable procedure, and explain what evidence resolves it. Manufacturer technical support may be useful where the procedure or part condition is disputed. Ask who will obtain that answer and when you will receive an update.
Do not remove a tag, reconnect disconnected equipment, bypass a safety control, or restart the furnace to see who is right. Ask the involved parties what restrictions remain while clarification is underway and what safe temporary arrangements they recommend. If the home cannot be kept safely usable, make a plan for people to stay elsewhere while the question is resolved.
The result you need is a single understandable record: the remaining condition, the permitted use or required shutdown, the next work, and the person responsible for confirming completion. A third opinion that simply says “looks fine” leaves the same problem open.