PathCare Harassment

I am very disappointed by the mistreatment and abuse that I am getting from Pathcare accounts department. A month ago I did tests at Pathcare when I was doing a procedure. Right after the procedure I had to make payment which I duly did. A week after, on a DAILY basis I am getting mails and calls from Pathcare Accounts Department harassing of non-payment. I am tired of this harassment yet I had to settle these people right after a painful precudure. Please advice me, I have been answering that I have paid and sending POP but they are not stopping, what options do I have.