XS rear glass smashed

Dropped my iPhone XS and cracked all the rear glass, however it was working fine...Until this week when i dropped it again and now the display/touch screen is playing up. It opens/closes apps randomly whenever it wants, areas of the screen are unresponsive at times, executes actions whenever it wants (when I'm typing a message it'll just send before i'm finished)......

I presume something inside has gone wrong. Can anyone shed any light on this?

I know Apple charge hundreds of pounds for a repair (almost the cost of a new handset) and I'm not prepared to pay such ridiculous costs for an issue they should have foreseen when they were putting this delicate model together.