******* service from collections department

I took out a smartspend loan with FNB in January 2019 of R7000, my agreed installment was R1638 for 6 months. FNB then went ahead and adjusted my installments into weekly installments of R412 as i get paid weekly. July 2019 was supposed to be my last debit month, then on the 12 July 2019 instead of debiting R412 as agreed they debited R400 then the following week 19 July R279 and then 26 July 2019 ( which was supposed to be my last debit date) they debited R200. when I called their collections department i was told that the system automatically reduced my installments, when I asked why I wasn't informed of the changes, the agent i was speaking to then went ahead and told me that it is my responsibility to check that information, i asked to speak to a manager but i was put on hold for more than 20 minutes. I now have a outstanding balance of R537 and no one wants to assist me they keep putting me on hold.