Unprofessional Staff with a bad attitude

We had a payment agreed upon by FNB (of which we have copy) that spread the payments over 3 months. To our surprise they not only pulled the full amount but pulled a double payment. When we requested them to reverse this they said they only would reverse the double payment and that would take 3 days. Even with the proof of arrangement they said they would not fix the matter and said we must live with it. Well we have subsequently cancelled this credit card and will be careful doing business with FNB in the future.