Windows Azure is commercially available in the following 84 countries, and this is not one of them. Learn more here: http://www.windowsazure.com/en-us/pricing/faq/
We are adding more countries as we can, but in the meantime if you wish to use the service in an unsupported country, you’ll need to use one of several third party providers which front the Azure Subscriptions for organizations in unsupported countries. Just keep in mind that those providers are not MSFT so perform due-diligence to make sure any vendor you select is reputable.
Thanks for understanding.Vichet Sen commented
It is 2018. Azure is still not available in Cambodia. Please add Cambodia as a supported country.