How to find corporate store

I have an issue I called in about and was told I would have to go to a store and show documents to resolve the issue.

I have gone to a couple stores but they are both agents and weren't able to help me. I asked them if they knew where corporate stores were and they didn't know.

I have called back in but both times I got a message that volumes were too high and I was disconnected.

Is there some way to distinguish between corporate and agency stores so I can go to a store to resolve the issue?