threatening me for payment

I was admitted on 4th just before 12pm and was discharged the very next day. Pre authorization was done the same time with my medical aid, Discovery. The hospital then goes claim for full 2 days. Medical aid only paid for 1 day stay. I was sent an email by the account department, which i forwarded to discovery who later paid for up to 1.5 stay. Still brenthurst comes and claim another .5 day from me. I have been calling asking to speak to case manager and no one from case managers takes my call. I don't know how you expect to bill full 2 days. If the hospital was fully aware with the authorization from discovery then why keep quiet about it and later try come claim from me?