flr m extension application refused put on 10 year partner visa! HELP

[Annadvik]

I received a decision letter from home office couple of days ago saying that they decided to refuse my 5 year route application extension for flr m ( second period after initial grant of 2,5 years) saying that they are not satisfied that I meet the financial requirement of 18600.
They mentioned that they put me on 10 year partner visa instead because I have a British citizen child from previous relationship.
In reality I have two children one from previous relationship who is NOT British citizen - my daughter and she applied with me as a dependent in this extension application. I also have a second child - my son from my CURRENT marriage who is a British citizen and who's father is my sponsor for flr m.
I'm confused to the decision letter as my financial requirement is 22400 instead of 18600 as they mentioned in the decision letter. And also they mistaken the child.
We also submitted all possible financial documents.
The story is we applied through category b. Only my husband works. He changed employer 2 weeks before the date of application.

So we submitted 12 pay checks from previous employer showing that he earned around 30000 pounds over last 12 months together with corresponding bank accounts showing wage payments.

Letter from previous employer confirming his employment how much he was paid and confirming all pay checks amounts.

His previous signed contract of employment

His current signed contract of employment stating that he has 39,5 contractual hours each week and that he is paid per hour £10,50 and plus £2.10 per hour shift premium.

Letter from current employer confirming his employment date started his position that he is on permanent contract his current annual pay which consists of 21400 basic pay and 4300 shift allowance which together makes gross pay of over 25000.

His first pay check from new employer which was quite low but it was only for 2,5 weeks of work.
I do not understand why the decision was made this way.
Was it something just confused the caseworker becouse of my husband work change or were we really not eligible to extend in current route?
I will appreciate any feedback and advice as we are devastated about the result and the prospect of starting the 10 years from start and loosing previous 2,5 years is very daunting particularly for financial reasons as the application fees increase every year so drastically and we were hoping to only have one application ahead of us being for indefinite leave to remain.