Just to add to what
@Benjamin *****
said. If you are actually still studying up until 14th October, you're good until then, then just go a week or so before to immigration, with a letter from your school saying you will stop studying on the 14th October. That will give you time to get ready to leave. Or apply for another type of extension if you have a valid reason. As he pointed out you are not on a visa, but an extension of stay. As soon as you stop studying, that extension is no longer valid. If that's the case, you are already on amnesty, and would under normal circumstances be in overstay and potentially trouble. But they have waived the fines for that until 26th September. Letting you stay until then.