Undelivered package / customer did not cooperate with transport company

[Brick_guru]

Hi there,

we dispatched from Czech to US heavy order ca 90 kg and the customer did not cooperate with FedEx / he should confirm some form because of duty/.

After two weeks was the package shipped back to us.

We didn´t have free returns so we had to pay shipping cost double time /ca 1200 € /.

We tried to make any deal with customer, but it was wasting of time.

He is asking for full refund and I have no idea why we should loose 1200€ for shipping.

who is right?

thank you