How can we make the CSA listen?

My partner has recently had a claim put in December saying he should be paying £58 a week for his son and this is wrong.

We have sent payslips that prove this and come under their stupid 25% thing and they still wont reduce payments – what can we do to make them listen?

Would be easier if there was a face to face service then could shove the payslips in their faces!!!!!

Thanks!