Hi. Did you flash ROM with SPFT? If not please follow this SPFT updating instruction http://community.umidigi.com/thread-11-1-1.html
And here all available ROMs http://community.umidigi.com/forum-132-1.html
Also please contact seller for warranty. Maybe they give you some satisfying warranty option.
Otherwise if nothing help you need dissemble phone and check screen connection.
If still not working correctly please order new screen https://m.aliexpress.com/search.htm?keywords=umi+london+screen#/
Please choose option starting from around €26 as this units including screen, digitizer and glass as one unit and this option is easy to fix.