My greatest advice is to do PAST PAPERS, PAST PAPERS AND MORE PAST PAPERS.
You may not enjoy them but they are a key to success in my book. Do maybe one a week or more if you're really dedicated then bring up the mark scheme after and go through and mark them yourself and then make sure to correct where you have gone wrong, focusing your revision on what you clearly do not know.
About your grades in mocks, you sound like you were in a similar situation to me when I was close to taking to real exams. I knew I wasn't doing well and I think you can see that too but that spurred me on to improve! As long as you are doing hard revision most days up until the summer exams you will be sure to improve your grades, I went up 1 or 2 grades and in some cases 3 from mocks to the real thing, it's definitely possible if you put the work in but you have to ask yourself, am I really trying or revising enough? I was literally the same as you but came out with 8As 1B and a D in Spanish which I didn't try for at all really which I kind of regret.
If you really are revising hard and still getting duff grades maybe change your revision style, instead of sitting with a textbook reading and making the odd note, look up some other and more dynamic revision styles. Although my favourite was always past papers as you can correct where you have gone wrong after.
There is no magic way to get the results you want apart from just putting the hard effort in and using your teachers for extra support where you are struggling.
I wish you the best of luck on your exams and hope to hear how you got on!
Don't give up!