I have the Samsung S10+. I have recently moved and my phone signal is not available everywhere around the house. I have tried turning on WiFi calling but the option under phone setting is not there. I have contacted my network and they have reset it their end but still no luck.
I think for your WiFi calling to work the S10 plus needs to be direct from Vodafone cause their stock has the correct firmware / software with WiFi calling installed. you can ring their technical team to confirm.
"All the devices on this page will support WiFi calling when you buy them directly from us. Please note that phones bought from other UK telecom providers are unlikely to support our WiFi calling, with the exception of iPhones, which should work regardless.
Devices might not be compatible when bought from third parties, we’re working with these other manufacturers to add our settings."