query on debit order

I am F*n angry about the bad service I received from credit card division ,I have made payment arrangement of R500.00 monthly debit order to be deducted on my account for FNB Credit card which was handed over to legal department, however recently on Tuesday a consultant phoned me to advise that he will be increasing my installment and I have told him that I will not afford more money to be deducted but he was persistent, I did not agree to the new arrangement, I can only afford the amount which we previously agreed upon R500.00..I am so disappointed and stressed about the manner in which credit card division have handled my account, I will also inform my friends and family not to use their service because they have a bad customer service