Netcare claiming we did not pay an account after a year and even though we have proof of payment

My wife gave birth at Parklane hospital on 11 May 2017. We moved into a private room and paid for the room upfront as required by the hospital. Over a year has passed and on the 16 May 2018 we get an account saying we did not pay for the room and that now I must send a proof of payment. We received no communication to this effect before this. I then had to incur the cost of going to the bank to get my credit card history which I have done and it clearly shows the payment was made. Carla Silijeur and Sarah Eavening who dealt with this matter are highly ***********. I don't know where they are transferring funds do and I hope Netcare investigates this.