Poor communication and threats from BESTMED

I've been with Bestmed for 9 years. I received earlier this year a sudden statement stating that i owe them R3k. I've asked for a descent statement indicating for what reason do i owe them the indicated amount. Not even from the statement could i see what the amount was for. In the interim i'm getting mails with final demands and that they are going to cancel my membership, but not knowing what i need to pay for. After various emails and request and endless mails i eventually get told the outstanding amount dates back to Sep 2018 when they double paid an amount to myself instead of the Dr. They then reversed 50% of the payment and paid the Dr and keep me responsible for the balance almost 2 years later for their poor book keeping.