Investment not paid in full

My father had an investment with momentum from 1992 and now it's time for them to pay out as the investment matured. He was paid less that what he contributed in those years and wasn't given any interest on the investment, what's worse they send a statement that doesn't make sense at all reflecting wrong policy number. Since they can't give him the money in full which is R64000, at least give him all his premiums back even if you can count from June 2005 as you claim the money given doesn't balance the years.