No PMBs Covered

I went to the psychiatrist as part of my PMBs early in August. This doctor sent in a letter to Discovery to confirm that he is my psychiatrist and should be claimed from PMB's. Discovery has always paid. Upon this visit, I received a statement from the practice stating Discovery will not pay any monies towards this consultation. I took this up with Discovery, via email AND telephonically, who ensured me they would investigate and get back to me. This never happened. Today, again, the practice phoned regarding the amount owed. The lady stated it may be due to the letter from the doctor expiring and that a new one was required. How can the Discovery personnel not have told me this? Surely they are the ones who should be aware of such matters? I am not going to pay this bill at all as according to legislation it falls within my PMBs. Discovery has done absolutely nothing to assist me. I need this matter sorted ASAP as I am looking to join a new, better medical scheme.