I didn't do anything bad whilst I was there and I am not sure if the Head lied about the Librarian lying about me or the librarian did actually lie and tell her I was told about the tutorial, when in fact I wasn't.
I have phoned and asked to arrange a meeting regarding me attending/coming back and she said that they had no spaces, so I asked about next year and she said that I have been told before that I wasn't welcome to come back for exams or lessons, then she just said bye and put the phone down.
I'd take it higher then. If you've not done anything terrible then they should give you a fair chance of getting your a levels and getting to uni.
I'm not sure who you'd go to to 'protest' as it were, but I'd definitely look into it and explain your situation.