Seek an attorney to help explain the terms of your 'Appointment Letter' to you.
If there's no severance package then its obvious you were deceived and blinded into signing an appointment letter you shouldn't have.
You are entitled to a month's pay in lieu, and pro rated benefits so if you don't understand the terms of your appointment then seek the services of a lawyer.
Come to think of it...NNPC will never drop a staff without a panel's routine findings...are you sure you're a staff?
God bless all the same,
Cheers!