"Missed calls from Apple Singapore [...] regarding order status: I ordered a MacBook Air M5 on August 19, 2016, and today I received 5 missed calls from [...]. I checked online and found that this number belongs to Apple, but since I'm in Vietnam, how can I get them to contact me back or get in touch with them?"
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Getting Info Elsewhere:
These are just user-to-user forums. You are not chatting with Apple here. No one here, one these forums, has access to your account (and that is a good thing, BTW). So, that is why to contact Apple Support Directly.
Chat with Apple:
As for contacting Apple Support, there is no direct way to do so via phone in Nepal. So, play a hunch. Go here and select one of your items: https://getsupport.apple.com/. Once there, troubleshoot for a few moments(ie Network Issues), and then say something to the effect… “Oh! BYW: I need to followup with Apple on an order. Can you please assist me with this?”