The word 'عاقبة' is read with both the accusative and nominative cases. 'السُّواى' is the feminine form of 'الأسوأ', which means the worst, just as 'الحسنى' is the feminine form of 'الأحسن'. The meaning is that they were punished in this world with destruction, then their consequence was the worst, except that the apparent form is used in place of the implicit, meaning: the punishment which is the worst of punishments in the Hereafter, which is Hell that has been prepared for the disbelievers. And 'أَنْ كَذَّبُوا' means because they lied. It is also possible that 'أن' means: that, because if the interpretation of 'الإساءة' is lying and mocking, it would be in the sense of the saying, such as: he called and he wrote, and similar expressions. Another interpretation is that 'أَساؤُا السُّواى' means they committed the sin which is the worst of sins, and 'أَنْ كَذَّبُوا' is an explanatory conjunction for it, and the predicate of 'كان' is omitted as it is omitted in the response to 'لما' and 'لو', intending to keep it vague.