I’ve had a couple of samsungs, won’t again. I like them but both have died within 12 months effectively, and always got crap signal compared to other phones on same network, also show signal but state ’emergency calls only’ a lot of the time. I’d try a new SIM card, then a new phone. Samsung only 12 month warranty as standard, most other android devices 24 months apparently. Both of mine suffered battery/power issues, turning off randomly, random battery life, inaccurate battery percentage indication, different models, years apart.
Just switched to second hand iPhone 6, it’s got no back button, which is a stupid idea, and is less intuitive, more restrictive, but better in every other way I think.