On going chaos with a client

Calls every few days from an office building complex. Going to skip what was going on for a month now, to last week... Our company suggested to replace all the thermostats with new, 7 day programmables. Gave a quote. Denied.
They bought the thermostats and installed themselves. (They have two 20-something year old maintenance guys)

Got a call saying no heat/ no cool. During the Tstat switch, they shorted some units' Transformers and Circuit board fuses. (Touching R and C)

We diagnose the issues, and give quote to replace the transformers. A few days later, we get another no heat/ no cool call. The transformers they bought were 75VA, instead of 40VA. The first one was shorted out. The second one would only trip it's built-in 3.7A breaker.

Now aside from the disaster that's been going on, I'm asking for help here. My boss wants me to keep going back to these boneheads despite all the unbelievable crap that's been going on. :gah:

I put in the proper 40VA transformer, with a 3A fuse inline. As soon as I turned power back, it popped the fuse.

I pop in another fuse, but this time, nothing, not even 24 volts.

I installed another, brand new transformer, and no 24 volts. The transformer's primary windings are, for sure, receiving 220 volts. I had wired it for 240 volts.

I wasn't getting anything on the secondary, low voltage terminals.

This whole thing has just been unbelievably frustrating I just want to scream. I left the job site early, I just couldn't think straight.