The notification is specific to Vodafone and Samsung phones - this does not occur in the same way using the same SIM and an apple device for example., and friends with the same phones and different providers do not get that notification. The issue is more annoying if you are using WiFi calling (which is a good thing) in an area with poor signal (such as an area with less signal strength or larger offices in a city environment) where the signal is intermittant and the phones are repeatedly in and out of signal. If you have other devices tethered to you phone the notifications are mirrored.
The answer lies somewhere between Vodafone and Samsung, i'm slightly thinking that its not a top priority for Vodafone as they would probably rather you did'nt use WiFi calling, and i guess Samsung are not in control of the notifications generated by the cell provider?
As the previous contributer suggested, there are ways of temporarily surpressing these notifications, however that only works until the next update.
I'm sure some of you really smart users will come up with a clever combinations of settings
