Old Mutual hasn't paid me all my pension

Some of my pension fund contributions were not added to my pension and when my pension was paid out I was able to see this only because I am an accountant and know how to ensure all contributions were included. I have been querying this for 2 months and Old Mutual has admitted on email that it is true and promised to allocate them and pay out the shortfall to me but they still haven't. I've sent a number of emails and spent a large amount of airtime trying to get assistance, to no avail. They are unable to phone me back and seem unable to resolve the issue as I keep get someone different on the other end and have to explain all over again. What would have happened to the money if I didn't pick this up? It would have stayed in a huge pool of unallocated funds and old mutual would have made a profit by investing the money and banking a part of the returns. How many people has this happened to without them even knowing???