I paid for an online course but I am not getting any service

I have paid for an online course after attending a webinar. The course instructor is not responding to my messages properly and the mobile number is switch off all the time. With a lot of difficulties I could connect with someone from his team but they don't want to return my money. I got no service for which I made the payment but they don't want to return my money. This way they are cheating so many people after taking money. Please advise what action should I take against them.