I stopped doing my EPQ as well after I'd received my offers (as I had made very little progress). You need to email the universities to ask. If they say no, and that the EPQ is part of the offer, then sorry you'll have to do it. Whit me, and hopefully you also, they said that the EPQ didn't count as past of the offer and if you would rather focus on the exams then you can drop the EPQ. You them need to inform UCAS so that they can remove it from your application form to avoid any confusion later on.