CODE ERROR NOT ACCEPTED

I was in hospital 6/8/2018 to 7/8/2016 a glucose blood test was done which was submit to my medical aid - Medishield. They rejected the claim siting 'Pathology request note required from the laboratory for code to be processed'. I phoned Pathcare and duly inform them of the problem. Pathcare resubmitted the account - J ********** dated 06/08/2018 which was again rejected by my medical aid saying 'Thank you for your email to query the account for Drs Dietrich Bruce E Street & Partners, practice number ********** and treatment date 06/08/2018, kindly forward an amended account for code number 4057 must be changed to code number 4050 to be reprocessed.' I sent an email to Pathcare advising them of the medical aid descision. I was promptly told by Simonay Piet of Pathcare that they cannot change the code and since my medical aid had rejected the claim as an exclusion, I was liable for the account. I cannot accept this as at no time was I advised by my medical aid that this was an exclusion and it is very clear from their email that the wrong code was used but I cannot seem to get this across to Simonay Piet of Pathcare who is demanding I pay the account. Well I am sorry we are all human and make mistakes and if she cannot accept Pathcare's accounts error then I am certainly not paying the account