Assuming that you have a 5G phone, your network setting could be set to “4G preferred”. Go to your phone settings and set your phone to “5G preferred”. On Android devices, this would be under the “Mobile Network” setting. Click on the SIM, and check your “Preferred Network Type” and ensure that its set to “5G Preferred”. On iPhone, go to settings, Mobile Data options and ensure that Voice and Data is set to the appropriate setting for 5G.
If the settings are correct, please ensure that you have purchased a 5G plan.