How would I claim my deceased sisters pension?

Mags1966

My sister died in 1998 leaving a will which was divided according to her wishes. She had a pension which she had paid into for all her working life which was from 16 to 41 years(which was her age on death). Unfortunately the company she worked for changed their pension scheme and made her nominate a person who would inherit her pension cash lump sum upon death, she had nominated my Father, who died only a few months before her. The argument from the Pension company was that her nominated person was deceased, therefore they would not pay out to any other member of her family not even my mother, even though they were her next of kin.
I tried to appeal at the time and took to an ombudsman but this was in the late 90's. I wondered if there was any way this could be tried at appeal again as many different types of claiming seem to take place these days?
I still have the paperwork as I thought there may be a chance one day. Has anyone got any advice or even heard of anyone winning in this kind of situation please? My sister had £14,000 saved in her pension.