Why won’t they reassess my wages now that I’m back from war?

Due to a marriage break up my ex took me to the CMA/CSA, when they calculated my annual wage through Inland Revenue, they took the annual wage I had whilst serving in Afghanistan.

Soldiers earn more whilst on operations, now that I am back in the UK and now earn almost £3000 less per year it doesnt matter, they refuse to reasses my annual wage even though they have it in front of them.

I will now be assessed on 6 years of £3000 that I physically dont earn, how is that fair??

There must be someone out there who has the power to tell CMA/CSA to get a grip and stop messing people around. I also just found out that the CMA/CSA will be charging me an additional 20% to cover the handling of the standing orders they do to my ex’s on top of the payment already.