Bad service

This is the third time I had to voice on this platform as I am not getting any joy from FNB and I am considering closing all my accounts and home loan. I had a Revolving loan which I settled in March the account was never closed and styed on my profile till last week when they removed it and sent me a settlement letter. The problem is that they wrote off the outstanding balance that they never closed in March now I am sitting with a write off bad debt review on my name when it was their fault in the first place.I can't qualify for credit because they didn't do their job correctly.