If your goods were exported by a shipping company you do not need to get a customs stamp. Instead, you should ask your shipping company to provide official export documents.
You can also provide official import documents from the non-EU country your goods are exported to.
Please make sure the correct information is mentioned and readable (english) on your export and import documents. Otherwise we can not process your claim.
If you export your goods by airplane or car yourself please read our instructions here.