unpaid severance pay

I was employed with a mid sized company for 10 years until my employment was terminated in 2014. I was on FMLA bc of my father's illness and was unable to return after the FMLA expired. I filed for umployment which the company initially contested and advised DOL that my termination was due to excessive absences. After I sent the termination letter to DOL, it was determined I was eligible as I was terminated technically for no cause. In any event, 3 years later I was cleaning my closet and came upon a copy of our employee handbook where I am entitled to severance pay which I was never advised at the time of termination and to date, have never received. I wrote the the head of HR about this matter and have not received a response. What is the company's responsibility re matters like this? Is it too late to as for severance? Is it too bad? or is there a penalty on their side for deliberately misleading or avoiding to pay this benefit? Thank You.