Galaxy s6 won't send/receive text/calls without 4g

[Necroparagon]

Hello, I've had my s6 for a few years now and have occasionally checked online to see if anyone else experiences my issue, though I haven't. In hopes of finding a solution I am posting here. My s6 will not perform network functions without LTE, and what I mean is, even if I have service, it won't work unless it explicitly says I have 4g. If it says 3g, 1x, or just regular service, I will not be able to send or receive texts and I won't be able to place calls. I'm sure you can understand how this can be extremely frustrating and I have no idea why this would be happening. If anyone can offer any insight, it would be greatly appreciated as this issue has plagued me for two years now. Thank you.