I was paying £150 a month child maintenance via CSA. They used my payslips to calculate what i pay. The CSA agreement finished on Jan 11 2017 and CMO took over. They used the taxable pay from HMRC which included my company car and fuel card allowance. This added an extra £8000 on to my salary of £26000. So my payments have gone up to £240 a month. Can my ex ask for back dated payments as she thinks I was hiding my salary from the CSA and giving an incorrect figure. I hope the above makes sense. Can you help?