Calls to my iPhone 13 are intermittently going to voice mail. It's a new Fido account. And some calls do get through. Why does it randomly send calls to voice mail?
Welcome to the community!
Is this happening everywhere including outside or just in specific areas? It sounds like you are having network issues.
You can try restarting your device and ensure your device has the latest updates including carrier services. If you are indoors and are connected to WiFi you might want to take advantage of the WiFi calling feature.