How long have you had the phone? It could be related to that the Network Provider does not service the phone.... Like with my moms non smartphone.... I may not be helpful.... But this is a possibility.. Abd with other old smartphones this may be the cause... A lot of times service providers stop servicing the old device simply to keep their system updated
i know a weird idea that worked on my touch screen phones and my friends i phone 4s, if you have a front plate put it or use earphones with a microphone