That's dreadful
there must be a formal appeal process where you can argue your case. I'd argue that you've been established on this treatment for 12 years - surely they can't just stop it? An appeal should listen to your reasons for increasing your A1c rather than just looking at a basic metric. I'd also point out that you've done everything they've told you to - you can't magically improve your HbA1c and "get your HbA1c down" is not a goal, it's a wish. If they haven't been supporting you by saying exactly what you should do to reduce your A1c then they can't expect it to be lower simply by giving you a pump (I'm making assumptions here based on my own experience). I'd contact your MP as well because ultimately the NHS answers to them.
Here in Aberdeen, they also make threats at every appointment - if you don't do whatever the latest thing they want you to do they'll stop your funding. It's always a "what" they want you to do rather than a "how" ... like "reduce your A1c by 1% in the next 3 months, without any mention of how you're supposed to do that. Luckily they haven't tried to actually stop my funding yet but if they did I would fight with everything I've got. Shocking that this seems to be a general culture across the whole country - it's ridiculous to threaten us when they should be supporting us.
Hope you get it sorted out - let us know. Standing there with you in solidarity if nothing else xox