If your buyer is being patient and understanding, I would ask them to contact the customs office in their capital city. Sometimes parcels can be intercepted, depending on what it is. Sometimes they can just get held up in customs for who knows what reason. I bought an item from China months ago and the tracking number says it's still in the sorting centre in the sellers city. The seller gave me a refund with no questions asked and if it does ever arrive, I will resend the money. Sometimes when you're dealing with Asian countries, things can move VERY slowly. That was in stark contrast to me getting a package from China 3 days after I paid for it!

Next time, send with tracking as opposed to sending registered.