disability insurance lump sum payment

I recieved a lump sum to settle a work comp claim. My long term disability insurer has reduced my monthly benefit by interpiting the policy's provision that ''if the period of time cannot be deterimined we will prorate the lump sum over 60 months'' It seems a no-brainer that the work-comp settlement is intended to replace payments for life and that the time for calculating the offset should be life.

The work-comp act in this case defines a settelment ''as commuting all payments for future benefits to a lump sum''

What recourse do I have to change this interpitation by the insurance co beyond appeal to the companies ''leader''?