I think that you have probably been conned into doing the work for free (the practice article). You may not receive payment and might have to chalk it up to experience. I no longer do free samples of a client's work – I'll supply them with a sample of my own work instead.
I would probably forget him and move on. I know it's hard, but do you really want to be working for someone who treats you like that? Don't give him any more of your precious energy and time. I would focus on setting up your own code of practice – making sure you don't do any work until a contract is confirmed, asking the right questions of the client, checking their profile before agreeing to work for them etc. When we are newbies and desperate for work, it's easy to be taken advantage of. Believe me; I've been in your shoes. Good luck.
Flag the job post and let Upwork know you were asked to work for free. You learned a valuable lesson. NEVER work for free! If he wanted a practice article, you reply: "I would be happy to do it. My cost is $x".
It simple and if he doesn't want to pay, you don't want to work with him.