Deeply disturbed by fraudulent CSA claim

I went to court with my ex and the judge granted a consent order in August which had £400 per child agreed as maintenance. I paid this since then and put it toward the mortgage on the house where she and the kids still live to which I have no access, mortgage is £1200.

In November she wrote to the CMS and they sent me a letter saying I had to pay, on top of the mortgage £1500 per month from 16th November in total. I asked how they had arrived at this and they said it was from my latest P60 provided by the tax office, however, they had used 2013’s P60 which I had earned £130k due to £60k of redundancy being in the amount.

Clearly this was a one off and I asked why they had not in fact used the 2014 (latest) P60 showing I had earned £80k. They had no explanation to this even though it was clearly wrong. I then found out by chance that CM cannot be claimed for 1 whole year from the date of any consent order with CM detailed on it, making my ex’s claim totally invalid and fraudulent.

I am now waiting for confirmation that it is invalid and fraudulent (they did ask if a consent order with Cm was in place and she said no). What I do not understand is that if I told them a lie I would go to jail, however my ex can make a fraudulent claim and the CMS do not seem bothered by the time, effort and ridiculous stress it has caused me for what in fact is a totally invalid and fraudulent claim by her.

Also I am deeply disturbed that nobody at CMS told me when I mentioned that I had a consent order in place that she could not claim, I had to find that out purely by chance. Surely the CMS should be fair and point facts like this out to both parties?