Hi - I'm a long-time lurker who's had a lot of fun and gained a lot of insight from reading all your wonderful posts so I decided to join in.

This happened a while ago, but I was wondering if I could have handled it better just in case I ever have any similar experiences in the future.
I had a job for a department of a public agency with a slightly confusing name. By way of example, I'll call it the Fruit Services Department of Tree Agency. The confusing part is that we only provided fruit services for Tree Agency, not anyone else. About half the phone calls we received were from outside agencies or members of the public looking for fruit services. I did my best to refer these callers to other resources that could provide them with the fruit services they were requesting.
One day, only a couple of months after starting to work at this particular job, I received a phone call from a lady with a very thick accent. I tried my best to assist her, and did understand a lot of what she was saying. But she kept referring to something, which was the main point of her phone call, that I just didn't understand. Perhaps she was using terminology that was familiar to her but not me (possibly due to language, cultural or geographic differences), fruit-related jargon I hadn't yet been introduced to, or maybe it was a simple misunderstanding due to the accent/pronunciation.
After about 15 minutes I still did not understand what she needed. I kept saying I wasn't understanding the terms she was using and she just repeated the same information. In other words, the definition of insanity – repeating the same thing expecting different results. Sensing growing frustration on both our parts, I suggested that perhaps an interpreter may be able to assist because I was having trouble understanding. She got angry (up until this she wasn't exactly pleasant, but she was polite) and yelled at me, “I speak English. I don't know what language you speak, but I speak English!” And then she hung up on me.
I still feel bad that I couldn't help her. Perhaps suggesting an interpreter was the wrong move, but I wasn't sure how else to help. At the time I was the only one in the office available to take the call. I suppose I could have taken a message but I don't know what I would have written down.
Any suggestions on what I should/could have done differently?