Rude behaviour

Hi I have been behind on my payments for about 4 months due to me not working Finally getting back on my feet and made arrangement to pay R 400 untill i get a raise Get a call from collections department and the agent was persitting i have to pay 450 kept telling the agent i can only afford 400 but she did not understand instead she become aggressive in telling my that i have to pay 450 I told the agent i can only afford 400 for now and if she got that extra 50 she can put it in coz i cant afford 450 right now she goes on to said that she didn't use the account i did and I have to pay 450

Agent had no way of talking or even tring to understand the situation And I already made a payment arrangement with precious agent and they seem to still call every few hours which clearly shows that they dont log the calls in