You are looking at the most elitist, most lucrative jobs in the City. You need Oxbridge LSE to land a graduate role. Don't believe the poison you hear about 'Goldman Sachs hire liberal art students/ uni doesn't matter' nonsense, maybe 1 out of 50 hires are from low-down unis and that's because they have inclusivity quotas. Also it's not just the UK, you will be competing against top Ivy league candidates and we all know how a uni's reputation matters because that's the first stage of slimming down the CV pile from 10000 to 1000.
Here are your options:
1- Re-do another year of A-levels and get 3A* if you think you can (probably involves paying for a grammar school and private tutors)
2- Forget about uni and apply directly to a bank's apprenticeship program (my recommendation, eventually you will need to do a Business master's but you saved yourself 3 years and 50k debt + 3 years of earning power which is like £100k net)
3- Go to a mid uni and be the absolute best student there, then try to get a Masters at Said Business School
4- Give up your dream and find an alternative, less competitive career path
I work in Finance (not gonna tell you where) and the above are viable paths people chose. Lastly most kids like you only seen the money side of things and not aware of the crazy hours they work to and the amount of burnout. There's a good reason why they only hire from top schools. People who can't put in adequate effort at A-levels are not going to survive the brutality of IB.