Passing the buck

I submitted a claim with ADMED on 13/03/2015 for the total amount of R4056.39 but my medical aid made things easy for them and paid a portion of this which was R1869.30 and so the balance of R2187.09 must be paid by ADMED but they are passing the buck and asking me for PMB which the medical aid stated on the claim statement that I was admitted at the time and they paid their portion according to the risk profile. ADMED simply running away for such a small amount claimed. This to me is bad service because they're the first to collect monthly premiums and have a lot of ducking and diving when it's time to pay.