MEDICAL(GEMS) FAILING TO SETTLE MY HOSPITAL BILL AFTER SOME 8 MONTHS

I went to the hospital after GEMS gave me authorization number, the bill amount was R 91,274.37 of which they paid R 87, 726.28 and I managed to settle the shortfall. On the 05 July 2017 they reversed the amount R87, 726.28 promising to settle the full hospital bill, but since July I have been waiting for them and my account at the hospital is sitting on R87,726.28 plus R3600.00 interests and they said the don't pay interests.