indebted father because of Old mutual

I had a problem with old mutual I have had my policy with them for more than a year now ,in this policy its me and my kids who don't use the same surname with me so last week one of my kids past away I submitted all the required documents then I got a call from claims department they requested me and the mother of the child to do affidavits confirming that I am a father of the child we did that then they sent me an SMS saying the want a marriage certificate or abbridged certificate or clinic card I asked them where am I suppose to get that for a 22year old who was not living with me full time,they said theres nothing they can do I must just forget about this claim.All my kids are not using my surname does this mean this is as good as not having a policy for my kids?and why was I advised that its not a problem for me even if our surnames are not the same then at claim stage they tell me this?