I have worked for Combined Motor holdings for 33 years

I have worked for Combined Motor holdings for 33 years. When I got my pension statement i realized that from 1990 till 2015 my pension was a mere R 419000 For the next 17 years it was R 1658000. I mean clearly there was mis management. I have contacted the pension Last year. Send them all the doc's what they required including my contract of employment. Just for them to send me a mail case closed. They told me can't go back from 2015 to 1990. This is really pathetic and bad. Thank you.