The equipment we supply is resold to the hospital, and the unpaid payment of the direct buyer disappears. Can we stop the use of the equipment in the hospital and how to operate it?

if the consignee only helps to complete the obligation of receiving goods, and there is no fault, it cannot ask the consignee to pay.

however, in your case, it is possible that the consignee and the buyer are in partnership for fraud. Please investigate carefully. If not, report the case first.