Threatening without consulting and delivering a service

On 6 December 2020 we visited LIFE Healthcare Groenkloof Hospital. I was advised more than once not to visit this specific hospital ever, but this was the closest hospital and it was an emergency. I am a private patient and we settled our bill on 6 December 2020 at the hospital. The receptionist on duty confirmed the total costs due and we settled the account there and then. In April 2021 we received an email that we have an outstanding account. We emailed Life Groenkloof Hospital to please send us a detailed invoice as we have already settled our account on 6 December 2020. No reply. On 20 July 2021 we received and sms that we have been handed over to Revco. Our legal team phoned Life Groenkloof Hospital to query the account and requested a detailed invoice by COB on 20 July 2021 - no invoice received. We contacted REVCO as well and requested a detailed invoice before COB 20 July 2021 - no invoice received again. Received another threat from REVCO today 21 July 2021. Don’t threat us if you don’t deliver any service as requested. I will take this matter further.