There's 2 separate issues here - the SN requirements + the exclusion..
Firstly where is the SENCO in all of this?
Do you have regular meetings with the SENCO?
Are you due any follow up review with the Paedeatric consultant?
What you need is school paperwork as evidence.. promises made, and not stuck to..
Re. the exclusion - what was the reason given in the letter home for the exclusion? was it an internal exclusion?.. A reason HAS to be put into writing to you ..
I know the 'will i make things worse' for DS quandary.. I wondered this myself.. but my DS cannot move schools, so long term it had to be sorted.
If you are worried about your DSs school record for the future, you can ask for a copy in writing to the head, and she is legally obliged to give it to you, within a certain time frame, so you can see what's in it. (i think it's within 10 school days, but you'll have to check)
I still don't understand fully why you are pursuing this, apart from pissed offness if your DS/D is due to leave.