How can I defend myself against my HOA demanding I remove a window from my townhouse?

I received a violation for a not approved window treatment on my townhouse.  The window was installed prior to purchasing the unit as with the previous owner.  This window has been installed more that 6 years before receiving the violation.  I believe there is a statute of limitations and laches may apply as this has been an unreasonable delay in enforcement.  My HOA brought in their law firm to enforce the violation.  When I explained my situation to the attorney he asked for an inspection of the window in question.  I met with the attorney, the general manager of the HOA, and the person issuing the violation for inspection and they determined that the window treatment was not a "film' as alleged in the violation and stated that it would be approved.  I filled out an application as a formality and it was approved. Months later I was advised that it was never officially approved and again I would need to comply with removing the window.  I went to the HOA with documents of the approval.  They did not have a copy of this approval.  There was a change in staff at the HOA and the new manager claimed that she was on leave at the time and that her signature was not hers.  I contacted the attorney that inspected my window for assistance who reached out to the HOA on the matter.  Shortly thereafter, I received an email from the HOA that the application for the window treatment has been approved and no further action was necessary.  Now 8 months later I received an email from the HOA law firm demanding that window be replaced and I pay all legal fees and fines.