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You're experiencing the phenomenon known as "ghost touch". There is electrical noise on the signal lines that carry the digitizer information from the touch screen to the processor, and that noise is getting interpreted as screen touches. Usually it's due to damage to the delicate connections between the flex cable and the glass the touch screen circuits are printed on. Unfortunately, separation or damage like that isn't repairable, so the only real fix is to replace the screen. Since the digitizer and display are fused together into a single assembly, you'll be replacing both at the same time.

This video will show you how to go about replacing your screen.

ITEL A70 - LCD SCREEN REPLACEMENT - CHANGE DISPLAY - YouTube

Although they're using a hot air gun to heat the front and back of the phone to soften the adhesive, an ordinary hair dryer will work for you; it just takes a bit longer to heat up the glue. Be careful to clean off all the old glue by scraping it off or using some 90% or higher concentration of isopropyl (rubbing) alcohol to wipe it with cotton swabs.