Notice of correction, or another way?

Naf

I'm assuming this is the best place to ask this.
Essentially I fear that a utility company or debt collector working on their behalf, is going to (or may already have) place late payment or default markers on my credit file - but the original cause of the situation is entirely their own error, and I have their letter which admits this.
I just want to know what the available and best avenues will be to get these removed if they do, indeed, go ahead. Or, better still, any ways I can try to prevent them doing it to begin with?