Don't let this happen to you!
You buy your barcode numbers online from a reseller, not their original owner or GS1. You affix your labels to your products and ship them out to Amazon or other retailer. Amazon contacts you and informs you that your numbers are not legal as they have been used before or the reseller did not have the legal right to sell them to you.
At the very least you will have to take back your products and relabel them. At the very worst, you end up in the legal system.
By buying directly from GS1 or from a GS1 verifiable original owner, like us, this could never happen to you.