Nationwide recovery service (woolworths)

On the 3rd of May I made contact with woolworths financial services stating that I am unable to make the payment due on my account on the 5th of May due to financial issues I encountered. I then proceeded to inform the consultant via the WhatsApp line that I will pay on the 28th of May but it wouldn't be a double installment. On the 13th of June I received a call from Nationwide recover services and I explained to the guy I spoke to that I experienced financial issues and and missed the payment that was due on the 3rd of May and I cannot pay a double installment. He offered me a payment plan that would run concurrently for 3 months. He stated that I should pay the exact amounts by the required dates as failure to do so will cancel the payment plan. On the 30th of June I made the fist payment of R1058. 85 as per the payment plan. In the second week of July is when all hell broke loose and I starter receiving calls from Nationwide recovery services stating I did not make payment, I then sent through proof of payment along with the payment plan to the email address they have provided. To date this matter has not been resolved. I still get calls every second day stating that I have paid, I even get harassed via email and WhatsApp that non payment is affecting my credit score. I am so tired of all the calls l I received as I answere most of the time as I work. I tell the consultants the same story all the time and I am then told I will be escalated only for me to get a call later in the day for the same issue