Talk with rep to file a non damaged phone claim

Half the screen working is usually hardware related.  If it isn't, a factory reset might fix it.  Not all forms of physical damage are visable.  Physical damage can also include the internal cable breaking from wear and tear, water damage, and more.  If you want to report it as something else, like defective.  I would give Customer Care a call at 611 or reach out to T-Mobile via DM on either Facebook or Twitter.