you could check your network settings and make sure you aren't set to 2G or 3G only assuming your SIM is a 4G or LTE type. Usually it's set to auto-detect or fall back if one network is having problems, but it's something easy to try. I'd reboot afterwards if you end up changing it. There are also a few apps on the Play store that will read a SIM and give you diagnostic info, probably won't help you but the info may help your carrier fix the issue.