Nedbank refuses to fix THEIR error with my credit

An ongoing issue for many years, I have just been declined a cell phone contract due to the fact that Nedbank REFUSES to fix their error on my credit report. I changed banks, due to Nedbanks pathetic service and after MONTH'S of them requesting to move the debit order for my Nedbank credit card to my new FNB account, they finally did it. I was in touch with a person, whose emails I should still have who had assured me they had removed the red marks off my credit report. This has not happened, it's been years. I'm seriously considering legal action against this lot, they lie through their teeth and it seems no amount of talking to anyone on the phone or over email will actually get them to do what they claim they're going to do.