Interesting as I have heard from other students at L3 that several have either been terminated or threatened with termination under similar circumstances, seems to be a newish policy. I suspect the true reason behind it is the massive delays in the flying programme (see other posts/forums) therefore if they can 'lose' a few students along the way so much the better. They are likely to be on penalty clauses for late delivery of airline (easyJet etc.) students (but not you) so anything to reduce the queue.
Full-time integrated ground school with accommodation etc. should be no more than about £12k so I reckon you should be looking for at least a £30k refund & no reason not to pay it. You would have thought even as a goodwill gesture they should be offering a substantial refund but they don't seem to have worked that one out. Their contracts used to mention 'guarantees', basically an insurance that provided you made minimum standards & things didn't work out you could get some of your money back? However if you started failing progress tests or real exams then this 'guarantee' would be revoked in writing.
In the UK only a court can actually enforce a contract. I'v known various companies write some amazing contract terms only to have them dismissed by an actual court. As said above get in touch with a lawyer asap, I can recommend
lawbite who I have actually used a couple of times on contract issues. You get a free 15 minute initial chat, so definitely worth a call.
Yet another lesson in don't go integrated (unless fully sponsored) & don't pay significant amounts up front.