Wrong Invoice

In March I went for blood tests, they submitted an invoice to the medical aid with wrong codes. I reported this to them and yes I was assisted, the invoice was amended and sent to the medical aid. We settled the account. Now they keep sending the wrong old invoice to me saying that the account is outstanding, I keep telling them of the amended invoice they sent us and we settled it but they choose to ignore it. On the 20th of June I called pathcare account and I was assisted by a lady who promised to update the account as she sees on her side that they keep sending the old invoice and that she will send me an updated account which is settled because I do not owe them. On the 21st of June I got sent the same old invoice stating that I still owe them and then I called accounts again to get this sorted and specifically asked for the complains departments number because now we going back and forth. They on the line just hanged up on me and he was really not interested to assist. I do not owe them anything. I have my records. Is this a ****? How do you amend an invoice and still require a person to pay the old invoice?