Discovery clawback money making scheme

I joined discovery in December 2017 until end of Jan 2018. I cancelled my membership with Discovery after January because of issues I had with the Medical Aid Company. 7 Months down the line on the 22nd of August I am contacted by a woman from Shapiro Shaik Defries demanding me to pay my outstanding clawback balance of R721.65. Until that date I have never been contacted nor have I been emailed yet I am billed for them "contacting me"? I would really like to know under which grounds is a clawback valid and how exactly do they calculate it.

Upon research discovery's clawback fine print is a common problem most people face with Discovery and I would never suggest anyone joining their Medical Aid Scheme because this is a complete ******* and a way for them to make money of you when you don't want to be affiliated with them anymore. They will exploit your wallet to their utmost best.