Sorry to hear about your experience. However, the one thing I think many people haven't given thought about and why Apple may be so hot on using credit to determine to hire someone. Every time I check out with any sales person in the apple store, I give them my credit card. They run the transaction right then and there. Who knows, maybe they feel if someone were financially strapped they would take the cc number and do some not so good things with it. I do believe if you pay with cash...shocking as that may sound, they would send you to the counter.
As far as your credit, do clear up any bad debt ASAP. Make sure they will help you clear your record on your credit report. BE sure to get it in writing and once you clear your record, be sure you get in writing that you have cleared up your debt and there should be no negative reports on any credit agency. Trust me, things have a way of reappearing. There is no way to clear up the late payments unless you can call and convince them otherwise. Sometimes it's best to close those accounts and let them fall off the report in 7 years. Remember a late payment is being more than 30 days late. If you fall to 60 days, it's really bad. Always make a payment on all accounts and never be late. IT really does affect your score.
Lastly, I do find honesty always works best. IF you know something is on your credit report, do disclose that during your first interview. If you have something criminal and you know it would come up, disclose that as well. IF they here your side of the story and not read a one line report it is much better. Most people have a forgiving heart when we hear the person admit to what their past was.
I hope all this makes sense. Best of luck on your search for a job.