Not to long ago, I was a temporary employee for the government (Census), and I need proof of it for my current job. I tried showing my pay slips, but they asked me for other proof. Problem is, I don’t live where I did the work, I live in DC now, so I can’t go by the census office there.
Call the office you worked for, ask for Human Resources, ask them for a letter confirming your employment. But I’m wondering why the Human Resources person at your current job can’t make the phone call themselves.