I'm on a low income and been having furnace issues...

I'm on a low income and been having furnace issues. I called Thompson and was quoted $87 for a diagnostics not including parts and labor but they wouldn't tell me how much I needed to have when they came out. So said fine come out run diagnostics I'll pay for that, so you'll know what's wrong and I'll know how much it is to pay to fix it. They refused to come out unless I could pay all in the same day without knowing how much. Not a good company.