My goodness I am so sorry to hear this; I can totally relate (not on the oxford offer tho aha no seriously well done for achieving that alone!) in terms of being crushed after opening the results, I was predicted 3 A*s for economics, applied to cambridge (but didn't get in) and received ABB this morning. I actually ended up not getting into any 5 of my unis and I was just too distraught to go into clearing.
For real it is crazy it's reckless. My advice however would be to keep your head up, make sure that you do go over all the possible options that you've got (I know it's generic but do) but mainly in this case, if you haven't already try asap to get in touch with your college's admit officer, or get your school to do it, and get on the phone to them. Explain and reinforce to them any your extenuating circumstances which may have lead the exams to go this way; and on top of how these exams were brutal in general too maybe. Tell them over the phone how much work and reading you've done for your A levels, almost like your selling yourself as you would do in an interview perhaps