Demands from a mgmnt co to which I have provided all requested info. What can I do to stop them?

I'm retired and live in a low rent condo. I installed an upgrade and have approval for it. I keep getting calls and letters demanding forms which were admittedly lost by the management co. I have provided what little I do have in support of my approval eighteen months ago. I need to have these persons stop badgering me. How can I do that?