Worst medical aid ever!!!

Discovery will not pay for a R8400 bill that they had agreed to pay. I got written authorisation from the medical aid for a procedure that i needed in 2020. According to the authorisation letter, i was not going to pay for no amount of R8400 and so I went ahead with the procedure, knowing that there will be no amount for me to pay. A few weeks later i get a call from the hospital saying i owe R8400, which surprised me obviously as i was not aware what this amount was for! I was not informed of this amount as it was not mentioned in the authorisation letter i got from this shady medical aid. I did the procedure on a Friday and i went home the same day as the doctor decided that i did not need to stay in hospital. The hospital in question is the Wilgers Life hospital and they should have been paid by Discovery per agreement. But this did not happen and i have been getting calls from the hospital and they have been threatening legal action against me for non-payment. This is grossly unfair as i was not made aware of the amount prior to the procedure. i have all the evidence i need, which accurately captures the sequence of events. On the Monday after my surgery, i get another pre-authorisation letter stating that i have to pay R8400, which was very strange as pre-authorisation should be obtained before any procedure is done. I assume this was a mistake on their end and i do not comprehend why and how i should be liable for their incompetence. i am extremely angry over this situation as it has caused me nothing but stress! Discovery needs to act right and pay the amount they had promised to pay. They called me some time last year and they were meant to get back to me in a week. They were supposed to update me regarding this matter and they did not. I am really fed up with this and I am willing to prove my case in court if need be. I will not be taken for a ride by some ******* medical scheme! i will not allow that at all!