decreasing my installment without my concerned

I had posted the same query on the 11 march 2015, i was called by one of the African bank consultant advising that she has change my installment to R200.00 every week, that only happened from the 20 march 2015 till 3 April 2015, last week Friday the 10 i checked my bank statement because i thought they haven't deducted, to my surprise they deducted R50 again and now my account is in arrears again, where can i report this cause it unacceptable.