Won a tribunal against the CSA but they still refuse to pay up

I was under the old system with the CSA and worked out that I had paid too much after discovering that carers allowance changed at different age of child ( age 13 & 16).

I was not informed of this when I was paying child support for my son. I questioned this and eventually took it to tribunal which which found in my favour but to my anger i received no refund because i did not inform them that my son had had a birthday.

All correspondence from them stated my son’s date of birth but the onus was on me to inform them. I overpaid by £3000+. Has anyone else had this experience?