What to say when calling DA office clerks?

I'm very new to being an assistant and my boss told me that sometimes clerk have an attitude and refuse to help. The problem here is that I am the least assertive person I know, lol.

Any advice on how to talk to them? I try to be polite to most people I talk to but I feel like that's not enough. What if they say they have a policy against sharing information? Should I push or let it go?

For reference, I'm mainly calling for the ADA's contact info for certain cases, or asking if they've received certain documents we've sent. Stuff like that.

Thanks!