CMS, keep using wrong info for calculations, claiming arrears

Joocyjoocy

- started university full time in September 2020. As a result, gone from full time employment to a zero hour part time job at weekends. My pay can vary, sometimes no pay if i dont have time available to work. 
- i sent them payslips from november to march 2021, where I averaged £102 a week for that period.

- they keep using a figure of £280 a week to calculate my payments. 
- ive sent the info twice. Asked for mandatory reconsideration the first time, gave all info again and they have again used a figure nearly 3x my average wage.

Not sure what else to do, for the timebeing I'm just using the calculator each weekly pay and paying the amount based on that.

- however, they are claiming arrears , based on the incorrect figure they are using. Saying i should of been paying  x amount based on £280 a month when that figure is wrong.