Discovery disregarding my payment plan

I experienced loss of earnings since Febraury 2019 and I had to cancel my Discovery health plan. I was then informed that I owe Discovery R1 919.12 which I had utilised in the savings benefit. I then agreed to pay R500pm until its paid. I have paid R1500 over the past 3 months to date. However I now discovered that Discovery has handed me over to attorneys regardless of my commitment to pay the debt off. I refuse to pay any additional fees that stem from Discovery handing me over to a collection agency since I had advised them of a payment plan which I adhered to. I await their response. Mrs RE Naidoo