Refusing to pay bill

My mum is a chronic kidney disease patient on dialysis and registered for PMB. Last year she was admitted to hospital many times and had a number of covid test done however during the second wave she was in hospital and just before she could be discharged the Dr requested a covid test because there was alot of presence of covid positive patients at the hospital. How ever medschield refuses to cover the bill unless a positive test can be provide, reason being she has used up the one annual test and have no available savings.