Terrible service with billing

Momentum medical aid has imposed co payments on certain medical aid options.i am on the custom option and there is a R1920 co payment. I was sent an sms and the hospital also requested the payment also an email confirming the same.I submitted the claim to my gap cover and they requested the documents from momentum confirming this co payment however no one can assist us ,they tell me there was no co payment required,then they resent me the authorization stating the same R1920 needs to be paid.Now the hospital tells us the medical aid has the co payment requirement and so does the sms sent to us from momentum. Then momentum tells us they didn't require a co payment ,and the gap cover won't pay something the medical aid doesnt show. So im R1920 short and I would like to be reimbursed my medical aid as they sent me the co payment details to settle.