Harassed for payment after arrangements made with bank

Nedbank handed me over to debt collectors who is harassing me to make payment on arrears but I have asked for a relieve of 3 months since I was affected by covid pandemic. They confirmed that they would extend the payment terms to accommodate my financial situation during the lockdown. Now I am being harassed to make additional payments to my existing instalment when I simply cannot afford it. I have explained this to them but they are persistent. This is unacceptable.