iPhone SE 2020 cellular reception drops calls

Hi, I’m new to apple products and puzzled why my phone gets such poor cellular reception. I have already changed the SIM with another provided by Verizon, reset network blah blahs, contacted apple and my seller (bought refurbished from back market), and contact Verizon 2 dozen+ times in the past 4 months. Daytime use attempts: can’t open app nor send text. Calls drop predictably. Late night use: crawls through tasks portly. Clue: I once had great V signal here…help. I am running 14.7.1 if that helps and tons of space-no clogging of space, 40+ gigs remaining.