iirc Oxford doesn't store data of applicants so you can reapply without worrying about anything. idk about resitting A Levels though, but I've never heard of needing extenuating circumstances? As long as you have email proof that the university told you that you wouldn't need extenuating circumstances for reapplying you'll be fine.
I found this post on some other social media of a successful Oxford reapplicant who had to retake an A Level too, it might help you:
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so uh i had this exact experience last year - i narrowly missed the grades for oxford last summer, and didnt want to go to my insurance choice (it was a fine uni, good course, i just didnt like the vibes and was so attached to oxford)
so i took a gap year and reapplied, my situ with subjs was weird but in the end ive ended up resitting biology
obviously got my offer again, and hoping to get the grade this time round
from my experience, pros have been:
obv another chance at oxford
being able to work and save up
being able to travel
still having a subject for some academic work but also having much more free time
recharging a bit after alevel burnout rather than going straight into uni
more time to research other options for the worst case scenario happening again
but obviously cons such as:
having to go through the whole reapplication process again with no guarantee of an offer
resitting exams sucks.
being a year behind friends
working out accom options (im living at home but have to pay parents rent)
stress of missing your offer a second time, and having a plan for if that happens
id suggest that it can be a great option, but to make sure you plan your gap year well before doing it - i hardly planned mine at all because i was so in denial for ages, and it ended up being really chaotic and ive hated so much of it
but you can definitely do it well, and end up at oxf next year
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P.S. You're not a failure! A Level results day was just brutal for us all. If you need someone to talk to, I don't mind being that person. (I'm an Oxford physics soon-to-be-fresher, but I was also very very very worried about my A Level grades and I had a sort-of gap year planned just in case my A Levels flopped.)