I'm sorry op you're having to fight for your child to go to the school you want. It is very common for Local Authorities to prefer to send a child with an EHCP to a state funded school as it's obviously cheaper for them that way.
As parents, you will need to advocate and fight for your child to go to a school of your choice. Can your preferred school offer any support or signpost you to any help? You have the right to appeal their decision, but it would probably be best for you to have someone who knows the system and what to say and do.