Accounts

I went to the emergency unit in May 2016. I got attended to by the doctors and a few weeks later they sent me the bill and informed me that my medical aid had not paid them because my savings had been depleted. However i made a payment plan and settled the amount. Today 04/04/2018 i received a call from Blake Associates. The agent told me i owe the Groenkloof hospital R915. I told him this should be incorrect as I settled my account. He gave me a number that i should call from Groenkloof hospital. I called them and I am being told i owe R915 even though i was never admitted to the hospital and i never received any invoice from them. The guy said i should escalate the matter with his manager. The people from Blake Associates called me again and said if i need an invoice i should give them my email address. I refused, you are saying you got my details from the hospital but you do not even have my email address how does this work? So i should just pay without seeing any invoice and description of what i am paying for? He then said i should expect a call from other departments more like threatening me that the matter will be pushed further. For an invoice i never received and payment i was never informed about? So why are they only telling me now about this 2 years later? And why should i provide my email address to people i never dealt with before ie Blake Associates i do not even know them and they want me to provide them with my email address? The doctors have my email where they emailed me the invoices how come Blake Associates only have my number? Why am i being threatened by an agent from Blake Associates?