Touch screen not responding in a region

Hi All!

I've returned my phone multiple times to HTC, but they sent it back every time saying they "do not experience the problem". Infact, after being off few hours it disappear for a little and then comes back.

A 1 cm horizontal region of the screen is unresponsive more or less in the upper part of the region where the keyboard appears. Which piece could I try to replace/repair?

See also this video that explain the issue:

https://www.youtube.com/watch?v=_vgtA6oi...

Thanks a lot!