Multiple in bound deliveries for single outbound

Hi

We have and exteransl SAP system(Vendor) sends one outbound delivery which needs to create single Inbound delivery in our system

But it is different .

For each outbound line item it is giving separate Inbound delivery for each line item(It is through Idocs)

After 30 Minutes for each line item it is showing 13 inbound deliveries in PO confirmations

Has any body have any idea how to resolve

Thanks in advance