The delivery address of your customers' items is irrelevant for a VAT refund. Relevant for refunding VAT is proof of export to a country outside the EU, obtained from European customs department. Alternatively, proof of import from Customs of a non-EU country is also accepted.
If export of the goods has been confirmed by Customs, a 0% VAT rate applies to the sale and you are required to refund any VAT that was paid at the time of sale.
You can read more about export and customs procedures here.