Sanlam Life - Investments (Withdrawal)

I am a sister of a Policy holder who is currently 12 year old. Last year August/September I took for him a tax free investment for rainy days and paid a lump sum, I signed the forms from Sanlam and they noted me as a Natural Guardian. I am the person who is taking care of my brother as they parents whereabouts are unknown. I submitted to Sanlam all the info they requested from me in order to open the account. On the 16th of March I made a request for Sanlam to make a withdrawal. Now Sanlam is telling me that I am not a natural/legal guardian yet 6 months ago i was told I am a natural guardian and they did not have an issue when i deposited this money. Now that I want to withdraw the funds it is now a problem. I am now being told because our surnames are different, I may not be the sister yet 6 months ago I was a natural guardian. This is happening in less than a year from the date I invested this money. They asked me get an affidavit and I did exactly but today all those documentation from inception are invalid. Sanlam is clearly ripping people off to benefit them, the marketing being done is not a true reflexion of what happens in the actual fact when people want their money. For many years I have been a good client of Sanlam iwith all my investments, life policies, company pension funds, funeral cover and after this I am done.