Good day administrator

Since I got my phone (Phantom) in March this year, I've had this sensors issues. The phone is supposed to go to off if I put it close to my ear during phone call and come back on if I remove it from my ear but it's not so.
2 weeks ago I changed the screen guard, because someone told me the screen guard could be blocking the sensors. after that day the same thing continued till now. it's either I use earpiece when making a phone call or the phone remains dead till I even have to beg who is on the other side to help drop the call.
this is the 1st time I'm having this issue with Tecno product.
I need help as to what I should do about it because it's kinda annoying and embarrassing.