CSA closed my case and won’t give a reason

After 9 yrs of applying for maintenance, in 2005 i was awarded weekly money plus arrears. Two weeks later i recieved a csa letter telling me my case was closed, no explanantion, nothing. I applied again and recieved a letter telling me i was awarded weekly payments and arrears from when i applied again, basically 12 weeks arrears. I called the csa today to find out where the money was, was told my case was closed, and given no reason.

I was told to write to the complaints dept and after min 28 days they’d tell me the reason why. My ex works, so does his wife, why can’t i get maintenance for my child?