Bad customer service

I received a call from Nudebt management on behalf of SABC license about an outstanding balance. I asked her if I could pay it in 2 instalments which she agreed and calculated an amount which she confirmed it will be R185.00. She also explained that if i'm late they will add R26.50. End of August I paid R185 which we agreed but September I was late I recived another call and the lady confirmed that I should pay R212.00 because of late payment. I went I paid that amount. A week later I recived a call that I still owe R98.00 I asked what is that for becuase according to me I no longer owe them, they confirmed that when I made a payment arrangment they added admin few. I told the person I am bot going to pay an amoubt I was never made aware of and why was it not included on the arrangment