School has intentionally messed up my grades to stop from going to other schools

You don't generally send mock grades when applying to other schools, rather you send your predicted grades which are often different to what you actually get, as they're calculated from a range of results. It seems to me that those are what you've been given?

I doubt that a school would purposefully change your grades just to keep you with them: especially as you've still got plenty of high grades, so you'd still be a good candidate.

our schools pretty much known for doing that, they’ve delayed notifying us about other school applications until late november (most schools in area have closed applications by then)

in the reference they’re sending mock grades too, and also it’s quite demoralising getting 8s but being marked down as low 6s.