Hi, I am so sorry your poor son had to go through this. It sounds dreadful. The school clearly were not able to meet his needs, and seemed unwilling to ask for assistance and support to put them in a position to be able to do so.
I think though that you have hit the nail on the head. If schools are prepared to lie and cover up complaints etc, it is very difficult. Taking on any institution is stressful, but one that is prepared to lie is doubly hard. Moving is best for your child, but, after you have moved, it seems to me that there is little you can do.
As I understand it, you can only make a formal complaint to the Governors while you are at the school. Did you try this while you were there? There is, however, nothing to stop you writing to set out your concerns so that it is brought to their attention. They are not, I think, obliged to respond, but, it would be good practice to do so.
I understand the circumstances in which the LA can get involved are limited and I believe (though you would have to check) that there is no direct access to the ombudsman against an individual school unless a child is statemented and you are at the school.
You can complain to Ofsted as this would fall under the grounds that Ofsted can deal with e.g. that the pupils? personal development and well-being are being neglected. However, you are no longer at the school so I don't know that Ofsted would puruse it, and, if they did, they would deal with the school on face value (i.e. they wouldn't investigate the specifics of your individual complaint).
I think you perhaps need to look at this not as a complaint in which you will be vindicated but as an awareness raising exercise so you can write openly to the Governors, LA, Ofsted, Head and tell them of your experience and how let down you were.
You might not see any action as a result personally but a reasoned letter like this should be taken seriously and will embarrass the school.