Maintance Payments Based Off 2012 TaxYear

I received a letter today for my child maintenance annual review. I am just going to state that my sons father is in a load of debt and his case is currently with the bailiffs due too constant missed payments. I read through the letter and realised I am still being paid the flat rate even though he has been working since October and we have no shared contact, so I checked from what year his earnings had been based off. (Something I haven't done before) turns out they have based these estimates off the tax year ending in 2012. Even though they already have a deduction of earnings set up directly through his employer and statements from HMRC. He has recently left his employment not long after a deduction of earnings was set up, something he has a history of doing, infact since my case was opened in 2014 I have only ever received around 5 payments all at the flat rate.

I called them straight away and the lady was quite confused herself, so she has put in a request for my caseworker to call me next week, and refused to let me complain untill this call. I am just wondering now if for the past three years my case has been set up, they have been working out his earnings from 2012, because he has had numerous other jobs within the past 5 years.

Any advice on how I can handle this situation? And possibly get someone to recalculate what I should have been getting all this time, because I have always been told I am only entitled to the flat rate of £7.00 per week.