Get something similar to this. BT 4600 Big Button Advanced Call Blocker Cordless Home Phone with Answer Machine https://www.amazon.co.uk/dp/B01CP2DT5I/ref=cm_sw_r_cp_apa_KIQ1BbWD7HPJ3.
Saves all the hassle. Got one for my parents who are in mid 80s after several "computer fault" calls.