Anycool T828 - Screen

Hi,
I have a problem with my Anycool T828: the phone has always worked very well, but from the last month, following a small fall (the phone, in fact, did not report any damage), the vision of the screen is not perfect as before, but it becomes more clear of normal, with shades of color almost iridescent and little contrast and I have to tilt the screen to get a clearer vision of the menu.
I precise that, for the rest, the phone continues to function perfectly; the only problem is the screen that switches, of continuous and without apparent reason, a perfect vision and a distorted vision in the brightness, contrast and color.
Why? What can have happened and what can I do to fix this?
Awaiting your courteous response, I send heartfelt greetings.
Sal