I was willingly paying my ex-wife more than the CSA rate for almost 3 years, for our 2 children, after our marriage ended... then my son decided he couldn't live with her anymore either, so went to live with his grandmother. Initially she said 'split the maintenance between me and my mother', which was ok for about 2 months, until she decided that wasn't enough and applied to the CSA. The CSA said it would be ok to include my son in their calculations, 10% to my ex-wife 10% to her mother (minus 2/7 for overnight stays, as I looked after them 104-155 nights per year)... this was until my ex-wife found out and informed the CSA she was still claiming child benefit for our son that was no longer living with her (she has also sent threatening text messages to her mother telling her she has no right to claim child benefit for our son). My ex-wife is only claiming child maintenance for our daughter, but that means she gets 15% for herself and I still have to provide her mother with money for our son out of what's left. The CSA say there's nothing they can do unless my ex-wife's mother claims the child benefit. Is this true or is this their discretionary judgement? The CSA don't appear to be acting in the best interests of both my children, just the one my ex-wife happens to be looking after. Incidentally, she has also reduced the overnight stays to get more money, but that's not really the CSA's fault.