MIBFA refusing to pay out

I am lodging this complaint on behalf of my mother , my dad passed away in 1986 he had a provident fund with MIBFA which she was unaware of. 27 years later she receives a letter in the post stating that funds had accrued over the years and gained interest the letter was received as my dad would have turned 55. My mum then visited the offices with all the necessary documents i.e. death cert , marriage cert and ID books. she was then told by a representative at the office that no payment would be made as we had left it too long. I have tried numerous times to contact MIBFA with no avail. Can anyone advise what steps we should next , I have read other complaints on MIBFA and it seems that there have been several issues with them.