Finished payment, but still getting calls saying I must pay

I was offered a discount on my FNB account, which I took then finished paying, I'm still having a problem of people phoning, emails and SMS's saying I'm still owing. Everytime when they phone they also say they can see I'm finished paying but they still not helping me get my paid up letter. I'm tired of being phoned every day and having to explain the same thing everyday. Can the supervisors please sort my problem out.