Legal department - Removing/ updating my CLOSED/PAID UP acc !!!

I have been trying for the past 2 months to sort out a closed phone contract to be removed from my credit score that i have paid up and closed a year ago. I checked my credit score and it is still reflecting that i owe them money but i do not. I have called the call center, which has put me through to their legal department who does almost next to nothing to help me, all they did was issue me a "paid up letter" and then proceed to tell me to check my credit score two weeks later, which i did and the amount is still there, I then called again to be put through to the legal department and all they did was provide me with a Cred Vetting number to call and to speak to them, i then called this number and it ask for that i insert my SS ID (which i have no idea what that is ), now you tell me Cell.c , How the f*** do i get this sorted.