For the newer people comming here : There is a new API called Slack Conversations API. Check this link as to why that is the case : https://api.slack.com/apis/conversations-api#conversations_api

The new API method to create channels is the conversations.create method: https://api.slack.com/methods/conversations.create

This method creates a public or private channel. 
It also returns an error for different cases, one of them is 'name_taken' implying that the channel was already created

Hope this helps :)