Beneficiary

Kindly pls assist, I have a Retirement Annuity Fund investment with old mutual since 2007 and the beneficiary is my sister in law. In 2012, I had my first child and I called them to change the beneficiary to my child. I received forms via email, I completed them and emailed back for amendment. Every year I receive RAF investment report and the details have not changed-it's still reflect my sister in law as a 100% beneficiary. I have a 2nd child now and I even visited 3 of their local branch and still I was told that they can't change it on the system. I have read all the documents that I have kept when I took the RAF but it does not state/mention that a beneficiary cannot be changed. Pls kindly assist as I have recently received the annual RAF investment with the same info even today??. I have cancelled the investment and the funds are still with them (I am aware that I cannot claim my funds as it exceeds seven thousand as per SARS law). Kindly please assist if they can amend the details to my children PLEASE PLEASE