No Letters on Sorority House

[britily18]

Hello all!
I am new to greekchat but i just wanted to ask you all for some advice.
My sorority chapter was recently re-established on campus about 5 years ago. 3 years ago we got our very first house. Although we are still the smallest chapter on campus we are growing rapidly (last year we had a pledge class of over 30 and am hoping to double that this fall!) The only problem we are having is getting letters on our house. Our nationals won't let us put letters up. Not only is this preventing our house from growing because pnms don't consider us a "real sorority" because we don't have letters, it also upsets our members and alumni because we have worked so hard to re-establish our chapter. On top of that nationals has told parents of legacies as well as alumni that we are allowed to put up our letters, but continuously tells our chapter that we are not allowed to.
Is there anyone that has heard of a situation like this or has advice on how to resolve the situation??
Thanks so much!