Paid up account

I have been getting calls from this company for an account that has been fully paid. I have been explaining to cunsultants calling me that this account is fully paid , i have been ask to send them a paid up letter wich i have emailled and even sent to their watsap as requested to do so, but still no difference they keep calling me still. Even 2 months later my credit record has not been updated with the credit buros.i find it very hard that people working for this company seems to be anproffesional. Please someone in this company needs to fix this thing, How can more than 50 people calling from this company and i explain one thing over and over but no one seem to correct any of this. Please fix this.