Harassment - One call back message received and 1 email a week ago

I have just received a call on my work line from a arrogant bully about a payment my medical aid confirmed they did not receive. I am bul**** and asked over my work phone during working hrs about why i do not answer private calls on my cellphone. I received first communication from them 18 Jan 2021 via email and 1 message taken from someone to call them back (1 time) and he is hounding me and threating me when i am telling him i cannot talk now and making me out to be lying. it was so unnerving and i was made to feel completely violated and harassed. I emailed my medical aid and they said they never received a claim from his client for whatever they are now charging me. Over R2k was claimed for other stuff for the same problem and it was paid and now there is more. I have seen this place once. I am beyond sick to my stomach. There is already over R300 been charged ontop of the account and i just dont know what to do? Why am i paying for a companies legal fees?