Account department treatment

My son had an procedure done on his knee on 28 February. I was told of the co-payment became there was a shortfall from the medical aid. I did pay the co-payment of the day.

A month after the operation I receives an email about the short payment of R1600, when I enquired I was told that there was an injection that costs R2300 and the medical aid okay paid R700, so I am liable for the shortfall. I then asked as to why am I being informed a month after the procedure and they said it was the medical aids fault that was not informed on time. I then requested for a payment plan since I have other medical bills I'm still paying for it was declined. A lady by the name of Khutso Rapo sent a follow email stating that she will handover my account if I don't pay by 6 May 2024. I find this treatment very unfair to be given only 2 months to pay the full amount of which I was not even aware of.