Absa trust fundEarly

Early dis year i went to my fathers work to findout if he had left any money for me and my siblings since he died on 25th March 1990 and we didn't recieve anything when we turned 21st. I was informed that there was money but it is with Absa Trust Fund no.*** I further went to absa and i was told that the money has expired in 1997 since no one come to claim. I humbled request for your assistance regard to dis issue because i don't understand how the money get expires.