This sort of shitty treatment of children with SEND goes on more than you'd realise, and I'd say it goes on in mainstream schools as much (if not more than) special.
I have 2 children with SEND and have experience of mainstream primary and secondary, a LEA special and independent special.
I removed my autistic 3 yo from a mainstream primary school nursery class because their TAs yelled at and manhandled the children unnecessarily. There were witnesses and cctv, but they still thought they'd done nothing wrong.
My elder child had some awful things said to her by TAs in mainstream secondary, and heard TAs gossiping about a girl with down syndrome whilst this girl and other children were in the room and could hear! Again I got absolutely nowhere raising concerns.
In fact the statement from the Wirral Life school doesnt surprise me, it is exactly like the gaslighting responses i got from both mainstream schools that i raised concerns to.
The independent specialist school did employ unqualified teachers which isnt great and i wasnt so happy about, but they were patient and kind to the children- my eldest definitely would have reported anything untoward! And I have had no problems with the LEA special school.