OP I think your focus really needs to be getting an entry level job before thinking about becoming a high earner.
Work with the job centre, take every course they offer. Continuously apply for work, go to every interview, take on any work that's offered, try agency work. Anything that will get you on the ladder and earning something.
Think about the transferable skills that you've already got - how do they apply in general life? What have you learned from your apprenticeship that you can use in other jobs?
Once you're working, even if it is part time retail or care work, take all opportunities there are to further yourself - even if it's a random online course found on groupon or the like - you'd be amazed how these seemingly 'basic' learning opportunities can help you work up the ladder.
Is there anything that really interests you? Any sector you'd really love to work in? Anything that you think you'd be really good at?
I left school with a C in English and an E in maths. I hadn't done any other GCSEs due to illness. I did 2 years of college arsing around with media studies and knew I didn't want to work in media - a couple of my cohort went on to get really good jobs, one did an apprenticeship with a regional TV production company and the other went to uni and works in movies.
For me, I worked in a pub waitressing, did care work for a while, then retail, went back to care work on an agency so that I could work more flexibly to go to college and get an access course under my belt. From there I went to uni and did my degree and although I wouldn't say I'm by any means a high earner, I'm comfortable. It's been difficult and while at uni we really lived in tough circumstances but we made it through.
DH worked in a food production facility as a nobody and worked up through supervisor roles and then trained in Audit before he was made redundant. He found another job in a different area quickly but hated it, so moved on. He's not yet in the job he wants but he vey bravely took a wage cut and a step down the ladder so that he had work to keep us secure. 5 years on and He's working his way back up slowly and I do believe he'll get where he wants to be but he had to make a big sacrifice to keep a roof over our heads.
His motto when made redundant was that it's either less money or no money; no point dreaming of the 27k he was on when the feasible options are 22k or nothing.
Keep your chin up OP, don't be disheartened by knock backs, just keep going, apply for anything and everything and grab any opportunity that comes your way. You can get there but it will take time and hard work. No one earns huge money without putting in a massive amount of time and work.