No, there hasn't been a "DIY thermostat replacement job".
Haven't had any problems for years, until about a week or two ago, a power surge caused a problem. The HVAC company was just there to fix that.
Seriously, is there something I can do.
Three people looked at it, it's set to 74 and it's freezing cold.
What did the power surge do to the system to cause you to call someone out? The service tech should have checked all before giving it the okay. Call them back to fix it correctly. If parts are needed you should only be charged for the parts..no labor charge if they are an honest company.
"Time to nut up or shut up!" Tallahassee - Zombieland