Source of supply deleted in shopping cart

Hi experts

I have in MDM catalog contracts from ECC, so user goes to catalog and serch for products and insert it in shopping cart, the system brings the ECC contracts as source of supply, my problem is sometimes the plant in shopping cart item is not the same is in item contract in ECC and must be changed and the source of supply is lost.

How can I make sure that the system always brings the correct plant in the item of shopping cart or the source of supply is not deleted when the was changed?

Thanks

Nilson