They work with debt collectors to make money off clients

On the 5th of August 2019 I received an email saying my account was handed over to Colmed, on the 6th I enquired with Samantha Davids why is it the case. On the 7th of August I made a partial payment towards the debt brought forward. I sent the proof of payment to Samantha Davids and informed her I will pay the outstanding amount over four months. She responded and said I (Samantha Davids) will inform Colmed about your payment arrangements. On the 29th August I again made payment and I forwarded the proof of payment to her of which she forwarded to Colmed. As she had done previously. On the 7th August She communicated with Colmed sent both proof of payment and the payment arrangement. To my surprise apparently I need to pay more money as charges had been accumulating as they say I refused to pay, how is that possible as Samantha Davids personally knew that Colmed is dealing with the debt and she personally informed them that the amount will be paid over four months and continued to send them proof of payment to say as promised this is the payment. Colmed now says I did not make arrangements, and Samantha Davids even cc'd on the email did not clarify that she did make payments arrangements and I(Samantha Davids) personally said I will inform you(Colmed). I didn't ask her to, she took it upon herself to I will inform them of the payment arrangement. She did not revert to me to say I didn't inform them or I forgot she happily took the second proof of payment and forwarded it to them and did not say in any given point in time that Colmed was not informed. I paid the full balance that was brought forth on the 5th August but now I am said to be owing over R1k, by law if payment arrangement are made the debt collector is not allowed to add any additional charges, since Samantha Davids personally made this arrangements I shouldn't incur any additional fees. So they now need to fix this with their people in 24hrs and give me my paid up letter, if this is how they trick clients into making money out of them it shall stop today. This is embezzlement at its peak, it's a premeditated act one that now results in me incurring R1k+ more debt. This is a money making scheme.