When Discovery makes you pay for their mistake!

As a student just trying to make ends meet I find my experience with Discovery shocking! I paid my premiums every month! Discovery made a mistake on their side by paying Lancet from my hospital plan and not savings. They only realized it 3 months later and reversed the payment to Lancet! When I phoned them they said it was a glitch in the system and it happens and I have to pay Lancet! I sent 2 letters to Discover and had no response! I phoned them twice and asked them to help as I am a student and it’s a lot of money to pay for a student and it’s not even my fault! They just said there is nothing they can do! I told them if that is the case I will have to cancel my policy to take that installment to pay Lancet! I lost my medical aid and vitality and had to be without a medical aid for a month! I am now getting letters from Discovery to say I have to pay them for canceling my policy. I have to take a loan just to pay this to Discover - when they made the mistake??? I think this is so unfair !!!! I don’t want judgments against my name !!! Stressed out student!!!!