Pay back of savings when resigning

I had to leave Discovery (that I was on through my employment), as I had resigned. They then send me a letter requesting me to pay them back for my allocated savings for the remaining months of the year, which savings I had already used up by March. No other medical aid has ever asked this even though I had left earlier in those particular years. It should be a risk they take having you as a member (and not voluntarily in my case), that you may leave before the year is up.

I will never go back on Discovery voluntarily and neither will my friends and family. Appalling that they request this money back when one pays way more in premiums every month, than the savings you get.