My partner tried 11 times to call me today. My phone didn't ring at all and I didn't receive any missed call notifications. We are both on Vodafone with two numbers on the same account. She got some nonsense message saying my phone was switched off or out of area. I was in the house, supposedly on WiFi calling as the signal is not usable.
The Vodafone signal is useless at home but WiFi should have worked. It is the posh version of Vodafone Broadband and normally quite reliable. She phoned from somewhere with decent Vodafone signal. If I can't reliably receive calls at home, the phrase 'as useful as a chocolate teapot' comes to mind.