Hi, I think there's a lot to unpack here do you mind sharing your results and what you want to go into? Also this notion of going to a russel group university isn't all that and it is much harder to do so without the traditional 3 a-levels with high grades at a-level and good gcse grades, there are also plenty of fantastic non russel group universities, I just graduated from a top 10 uni not in the russel group also again it also depends on what course you want to do as some non-russel group universities may even be better for that course or due to industry links etc.
As for your situation right now, I had my gcse maths marked incorrectly (and my entire grade went up when they marked it properly -__- ) so I couldn't do some of the a-levels i wanted too. However I was fortunate that my parent managed to drive me around to local colleges in the area as my gcses grades were good especially in the sciences which is what I wanted to do, and one of the colleges/teachers could see how upset I was and that i was smart so they let me enroll onto the a-levels I wanted to do. So as someone said negotiating with your college/sixth form and others is the best idea but i think it may be too late now as you are in november?
It's still worth asking just tell them you're really upset and want to change stuff around etc but it may be too late now but i'm guessing your in year12 if you don't act now it may be too late and you'll have a lot of catching up to do so be prepared to work hard, but I fear it would be very difficult now.
As for retaking GCSE's this really won't be allowed and neither is re-taking a-levels unless you have extenuating circumstances. I did have extenuating circumstances for my a-levels but I ended up not retaking them as I got good grades and the reason I bring this up is that you may need to look for alternative options to get into university for the course you want to do. I ended up getting 3 a-levels but ended up having to drop maths because of my personal issues so I applied to 'foundation years' at a couple of universities as I wanted to study physics and I got into university.
This is another way to get into a 'top' university but it isn't easy ( i got rejected from some despite good grades and extenuating circumstances) and you will need to contact some universities to ask them, how to get onto this programmes and how to stand out etc , the more a-levels you have the better, especially if you want to get into russel groups.
I think the most important thing is you figure out what you want to do / and choose a degree that leaves your options open a little bit so nothing too specific, i wouldnt do RS at degree level unless it's your passion and i'm not even sure what roles you could get from that but you've got to do something you like. Once you've chosen this speak to your college asap and try to see if they can guide you further on how to get there / if you can change what you are studying but i fear it may be too late.
There are also plenty of upcoming and decent non-university options, I left college like over 5-6 years ago now and longer since school and there was literally nothing available like T-levels etc. As someone else mentioned IT degree's not that they are bad but i don't think there will be any at russel groups?
But yeh unfortunately you aren't in the best position, so it's about finding alternative options and seeing if your school can do anything. The degree apprenticeship is a really good idea or an apprenticeship, i know this is sad to hear but don't dispair but you need to start taking action now and you can always take a-levels independantly but i don't know much about that but something to look into, but yeh i don't reccomend doing a degree if you don't need a degree for that subject as it's usually not worth it especially if there's no jobs and it'll be a waste of time and money. You may be better off doing history or english rather than RS but again jobs.
I've written a lot so i won't type anymore but if you have any questions feel free to ask. You may have to take a longer and more unconventional path then others but that's ok the earlier you do something about it the better. I also really reccomend speaking to a teacher you are close with, careers advisor. I just think your current choices a-level business, a-level RS and btec IT is a weird combo, i don't know how useful RS will be either. However if you are stuck with them then keep figuring out and alternative way to get to what you want to do.
remember a russel group university isn't all that, and neither is going to university also keep apprenticeship and other degree apprenticeship options open, there are many people now living fulfilling careers through this option many of those better of than those who did degrees too!