Global Post label switched?

We’ve been selling on Amazon 14 years and this is a complete new one to me.

We had an international order to Spain. Customer emails us, with photos, that he received a completely different order, different product altogether, intended for someone in Canada. We get international orders so infrequently, I don’t have enough experience to know if there’s any sort of way of requesting a lost mail claim through Global Post, or what a resolution might be. I assume even though it wasn’t our screw-up, we’re still on the hook for making it right to the customer (i.e. refunding the order)? Any advice here? Thanks.

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