Unprofessional Harassment

I'm flabbergasted. I'm not a person who leaves bills unpaid for months on end. In February last year, I went to the doctor for some routine tests and she arranged for my medical aid to pay for them, assuring me they were covered. So, I went away from the appointment without a worry. Lancet phones me a week ago saying I owe them R300 from these lab tests. So this is 11 months later, and then they spam me with about four copies with this account that my medical aid never paid for, which I had no idea about. I'd never received an invoice or statement previous to this date.

I had planned to pay this in a couple of days when some money had come through. They phone me again today saying that I have to pay it by the end of the month, like I'm going to be taken to the cleaners if I don't. I asked them why they hadn't told me about this outstanding account from February last year. What if I didn't have the money for it this month? She said that they've been phoning me since October. This is a total lie. I haven't had missed calls from Lancet, no emails, nothing. They have no reason to harass me like this because they are so slow in dealing with their accounts. They make a responsible person feel like a shirker with the way they speak to me. They treat me as if I've received multiple accounts since February. It's very insulting and unprofessional.