Payment arrangements not honored by FNB themselves

In the 3rd week of December FNB contacted me to arrange payment on my overdue credit card. I arranged with them that I would pay R1000 to them by the 15th of December after having received my salary. This arrangement was supposedly captured, with the condition that should payment not be made, summons would be issued against me and I would be handed over to the debt collectors. I did then pay the agreed amount on the 15th of Dec. When receiving my FNB statement this week, I saw that the amount owed to FNB is now R0.00 and the full amount owed has been 'Transferred to Legal'. Why does FNB phone clients to make arrangements if they do what they please in any case, even if the arrangement had been honored? This is truly concerning and pathetic service. Having lost my job, I am also indebted to ABSA, yet they have not gone to these extreme lengths even though the amount owed is much greater than that of FNB. I need answers as to FNB's irrational and overhasty decisions.