@Trisw because your data and text is working fine, it sounds like the issue is likely to do with VoLTE, not quite sure if the iPhone SE supports it or if it is on Public Mobile's white list of devices. Either way, try manually connecting to T-Mobile and if that doesn't help then try changing the network band to 2G. T-Mobile's 2G network (where available) is the only option for devices having issues with VoLTE
My wife had this issue a few months back. Even though her Samsung phone supports VoLTE, Public Mobile does not have it on their whitelist so she was not able to make or receive calls. For us, the work around was to just use Whatsapp and FaceTime. Other apps can be used for making calls like Facebook's messenger.
