Discovery Health withdrawal horror

I have been a member of Discovery Health for the past 20 years and I have changed employment twice, but have been on the same plan and using the same medical aid number. I resigned from my job last month and I joined the new employer on the 6th of May 2019 and we are in a process to get me back on the same medical aid and suddenly I am receiving notices from Discovery that I owe them money, which the consutant Malanwe said it was for money allocated to be and my benefeciaries have spend for the year. He sent me a statement that says I owe them money for 2013 which I did not know of. I was planning to go back to Discovery , but I am disgusted with the way they treat clients that withdraw from the fund. They also mentioned a draw back clause, which I asked Malandlwe to retrieve my contract and highlight the clause for me. Discovery is a very soar loser and very unprofessional. This is how they treat clients when they withdraw from the fund,I am wondering did they not bring the outstanding fees to my attention for 6 years they kept quite about them only on withdrawal.