Inventory Error

When I create a document, the code comes out wrong, for example, I am doing an inventory, I type the code 1001 and the product comes out, but the code 950, for example. The product is not confused, but as a picture, another code comes out. And another thing, how can we make it so that when an inventory document is created, every time it asks for a barcode to add a product if the quantity is to be added, not like now that it comes out, "Product exists." This type of form that is current does not help. If we do it like that, it looks like the palmar takes more quantity. Thank you