Name change as don't want this linked back or picked up by The Sun.
Looking for some outside perspective on this as I think we've got overly emotional.
Background info
DH has a child (11) from a previous short, casual relationship. Child maintenance by private arrangement since birth, currently £500pcm and has been for 2-3 years now. He uses the calculator as a guideline and rounds up to an easy number.
Child's mum got in touch and said she's struggling and needs CMS increased to £700.
The issue is, in the last couple of years, we've had children and DH has dropped hours to reduce our childcare bill. He was the higher earner initially, but I then overtook him and his job is more flexible so it made sense for our circumstances. The CMS was never reduced, wasn't really considered because we work from one pot, it's a non-negotiable outgoing, it was just left as it was. However, based on his current situation, when he checked the calculator said he should be paying around £330.
He got back to child's mum and said he can't increase to £700, he'd need to stay at £500 and then reassess in September when our childcare reduces. All hell has broken loose.
He's now saying screw it, go through CMS and pay the £330.
Child's mum is saying it needs to be £700 or she's "taking it further".
I'm just lost on what to do. I know it's not my issue to sort but he's my family and we're a team, I'm also a mother and don't like to think of another mother struggling. AIBU for wanting to push for it to remain at £500? Or should I step back and leave him to his knee jerk reaction of the CMS route? Is there a middle ground we've not considered?