@NonplasticBertrand in my experience of secondary schools, there are two types - those who do everything they can to support vulnerable students, and those who do their best to encourage parents to remove their children if they take up too much time / resources / effort... Only you will know which of these you have unfortunately!
If it is a systemic school wide issue, then the legal route is the only way to make them comply - bare minimum they can get away with weeks to be a standard approach sadly. If, however, you feel that the school are generally good,.then actually a formal complaint may be the way to go. Often I hear that the Sendco is unwilling to do x, y and z. But a formal complaint is heard by someone higher up and they will often ask why these things are not being done. I often speak to members of staff who are unaware of what other members of their team are telling parents, and while awkward, a formal complaint raises this issue and ensures.that other members of staff are forced to justify their decisions.
However, this all supposed that the EHCP is written in such a way that there is no doubt about the 1-2-1 hours?
Regarding the punishment for disability related stuff, it depends what it is. I have had success with taking school policies that were badly written and physically highlighting all the things that they cannot do due to disability. Where homework is not completed because the teacher didn't follow policy of adding it to the homework app, I have challenged this and had the behaviour points / detentions cancelled and teachers reminded of their responsibilities.