CORPORATE PHONE NUMBER FOR FIRSTNET

I have been dealing with FirstNet and a return since the end of June, beginning of July.  FIRSTNET is HORRIBLE!!!  I have submitted case upon case only for FirstNet to cancel them for incorrect routing or incorrect case details.  I have spoken with FirstNet customer service and supervisors who are unhelpful and cannot seem to get my problems resolved.  I have asked for a corporate phone number for FirstNet and have been told they don't have a corporate phone number to give me.  I will slowly move up this chain to get my money refunded and my upgrade eligibility reversed even if I have to get an attorney involved.  Can anyone provide a CORPORATE phone number for a supervisor, and NOT a customer service number.