Exactly the same thing happened to me in Muang Thon Thani.
Luckily I checked the paper whilst in the car outside the building. Went straight back in and to the officer who dealt with my report. He was very apologetic. No sign of the guy who’s form I had been given.
To update on this, despite what it says on their website, no proof of income was required. I emailed the embassy in order to obtain some clarification. The reply came back (within a few hours) listing requirements. All as per their website, with the exception of proof of income of which there was no mention at all. Went up the following morning, applied for visa and then collected it 24 hours later.
Yes, this may be one way around the problem. Not necessary to show monthly income, just 800K baht in bank account. Although I am under 50 so possibly not allowed to apply on grounds of age.