I also highly recommend looking up the name of the company president, and/or the senior managers.
Rather than asking to talk to "your manager", if you ask to talk to "Randy", they'll be a little more willing to play nice
And you can ask their operator to connect you to the boss directly if need be.
They don't need to know you're
not actually on a first-name basis with their boss or the president. They just need to give you what they owe you.