Claim for pre-authorised procedure paid out of savings by Momentum (their mistake). Two months later it still hasn't been resolved.

I terminated my Momentum Health membership in June 2017 because I had to change medical aid due to taking up new employment. In November 2017 they let me know that I owe them just over R3,5k. Upon inquiry they said that it was because they paid a supplier out of my Health Saver and it exceeded what was available because the full amount had been advanced at the start of 2017 and I terminated my membership halfway through the year. The payment was however for a procedure they gave me pre-authorisation for so it should have been made out of major medical. I made them aware of this more than two months ago but they kept sending me threatening SMS's and have now reversed the payment to the supplier. This despite finally sending me an email on 8 January 2018 stating that the payment would be processed on 19 January 2018. The supplier wants to hand over the account now because it's more than 120 days old.