Help troubleshooting heat + thermostat issues

We had our attic insulation replaced this weekend. They finished adding and sealing cracks sat afternoon. On sat evening, we noticed our Nest thermostat on our first floor stopped working saying c wire issue and our heat stopped.

The attic guys came back Sunday and found nothing unplugged or wires cut. They sent a friend who is an electrician to try to figure it out and he said we needed a new Nest unit. We installed the unit with him today and it still didn’t work. He thought it needed rewiring from the boiler and did that to no avail. The nest looked good but did nothing for heat.

We then had an hvac guy come to look. He told us there is no power connection between the boiler and that thermostat. He also said the only wires from the thermostat run to the AC unit in the attic and that it could never have provided heat bc there is no handler there. We have baseboard heat.

Both told us that our wiring was crazy.

I know for sure that we’ve used that thermostat to control the heat on that floor for the last 4 years we’ve lived here. Timing with the house work seems too suspicious to say they are unrelated events.

Does anyone have clever ideas on how someone might have connected the attic hvac to the boiler to the thermostat?

I want to push them to try to fix the issue without tearing down our walls which they are now suggesting.