You say you didn't enjoy your first year, is this because:
You felt like you settled for "second best"?
You studied a different course from the one you have taken at Oxbridge?
You don't like the location of your current university?
You haven't made friends because you didn't want to be there?
Before taking the drastic, very high risk strategy of dropping out and retaking for Oxbridge. Consider this, first time round without your A level grades being known you were rejected at interview stages. Since you are considering retaking your A levels, that suggests you didn't get A* across the board. You are required to list all your exam results on your UCAS form, so you will have your first time A level grades, potentially your first year university grades and your predicted A level retake grades. You would need to have the most compelling personal statement to explain your educational career trajectory to date, to convince an Oxbridge admission tutor to give you a chance over and above other students applying for the first time. You might get lucky, but given the competition for places, as a home student, the odds are not in favour.
If it is the course that is the problem and you have passed sufficiently well 2:1 or better level. See if you can transfer to a course that you have more interest in. A qualifying Law degree is a subject which teaching style and prestige are the significant variables. It might be worth contacting the university careers service and taking some tests to see what you be best suited to do as a career. From that you can work out what degree might suit you better and see if you can transfer to a more engaging course. If you have identified an alternative degree, the get the course outline and reading list and see if suits you.
If mentally you felt you "settled", this may have affected how you feel about your current course and university.
If you are doing well on your course inspite of your other issues. Finish the degree as well as you can and apply to Oxbridge for a post graduate course. Make the most of your time at your current university to ensure that in your post graduate application you come across as an outstanding student.
Consider carefully if you can afford to drop out and retake. How will you feel if having dropped out, funded your retakes, you still don't get that Oxbridge place? Will you be applying elsewhere because you still want a degree and end up at another university similar to your current one in a years time, instead of starting your final year at your current university?
Dropping out to chase an under graduate Oxbridge dream (given the increasing cost if higher education) is not something to be done with a great deal of thought. Only you know what you will be able to live with long term if things don't work out for you.