Hi
stringbeans41Thank you for your asking. Kindly provide the information below so that we could better assist you.
1. Your current firmware version
Setting >System>About Phone>Software information
If you try to update to the latest version, does the issue still remain? Could LTE and 4G work before update, and which version could LTE/4G work?
2. After you try change sim card, couldn't they works? Could you tell us the name of the carriers you've tried that have this problem?
3. Have you tried to open/close Volte?
Setting>Network & Internet>Mobile network>Advanced>Disable Enhanced 4G LTE Mode
4. What's your preferred network settings? (2G/3G or 2G/3G/4G)