Discovery medical aid nightmare(***)

I was on a savings plan- Essential delta saver with discovery from January to March 2021, I then changed my plan to Key care plus plan. what is annoying is when I changed the plan they did not explain to me that I will have to pay back the medical aid savings that I used. I received a call yesterday that I must pay R2800 back while I pay R2450 every month towards my plan. I have been with discovery for over 5 years now and I hardly use my benifits.