Unfair Blacklist

I had the Avon account some time back. However 2 to 3 years ago I paid Avon and cleared it. To this day is showing on my credit file with a mark. I am currently loosing good jobs due to Avon. I have been calling them to get this mess sorted but to this day nothing. I called them yesterday to speak to them about this as usual. I have been told that within 21 days it will be sorted. The most painful things is I am not getting credit account or jobs coz of this company.