The Local Government Ombudsman issued a report last year you can download from their website called "out of school out of mind". It puts minimum full-time education for a 12 year old at 24 hours.
But you are right on top of that actual education time he is entitled to leisure and social opportunities which should be provided in school with 1:1 but you could also argue as this is not being provided by school that it should be provided out of school through social care support e.g. direct payments to support leisure opportunities.
It is also discrimination if there is no reason why he cannot attend except financial. If they are not saying he would not manage a school day even with FT 1:1 then its clear discrimination as non disabled children are being offered a FT education.
The council should have emergency extra funding they can provide to any school that says it cannot afford the extra 1:1.
And you can ask to review the statement etc as above.
But yes its time to put your foot down, they have had long enough. It is not your problem who funds the support. If he needs FT 1:1 then it needs to be provided it is not your problem how this is financed. And I would insist as a minimum on the extra 2 hours as private tuition and a social care assessment to look at your needs as a carer and his needs as disabled child who is presently being denied any social opportunities until he can go FT.
When you moved the new County should have undertaken its own review of the statement and that should have been completed within 6 months. So you need to push for increased statemented hours and appeal any refusal to reassess / amend the Statement at next annual review.
You should at least make a formal complaint to the Chief Exec of the Council that this has taken so long - that then gives you the chance of going to the Ombudsman while you wait for any appeal to go through. On the basis of the LGO report they would be expecting a Council to offer FT, or if the child cannot manage FT ensuring at least 24 hours a week education.