Can't work out a correct settlement - Continues back and forth after you make payment!

I requested a settlement letter and had no trouble receiving it. Paid the amount as per the settlement letter. I've been battling to get my paid up letter. Eventually 8 days later, all of a suddend received another letter stating there is still an amount outstanding. Was is the meaning of you settlement letter? How does your settlement all of a sudden change? This is not the first time I'm facing this type of challenge with Standard Bank. I never want to deal with them in the future. Dishonest and unreliable! This bank deserves no stars!