Legal threats from Life Westcoast Private Hospital

I visited the Life Westcoast Private Hospital in July 2020. They put in a claim with my medical aid for the visit and that was the last I heard from them. I got a notification from my medical that the claim was submitted. Today get a final demand from the credit department at the aforementioned hospital saying they have sent me numerous requests for the payment of the account which is complete nonsense as this was the first email I had received from them. I contacted my medical aid to find out why the account hadn't been paid and they told me that they received the claim but they did not receive a request for authorization from the hospital. I spoke with a consultant on the phone and queried the threatening letter and she said that they had sent me one notification in November 2020 which I never received. I asked about the other numerous notifications and requests and was told that there was just the one. I fail to see how one attempt to contact me via email is seen as numerous attempts. They have my contact numbers but I received no calls from them. I don't have anything positive to say about this particular hospital or the people responsible for their accounts. They are completely ***********.