I've split this post off into a new thread, it was going OT for the previous one and this way, @Mel1407 can have replies specific to their predicament.
WiFi-calling is fundamentally an extremely reliable service and as capable of stable clear calls as the 4G-mobile network is. But network design is such that, except on some Android phones where the preference can be toggled, mobile network coverage will always take preference - and it does rely on a good wireless signal. If some of these conditions aren't met, it can give the perception of WiFi-calling being unreliable, when the fault lies elsewhere.
Depending on the nature of your phone repair, I wouldn't rule out a device issue - having seen users have very similar symptoms to you, their post-repair phones had all the symptoms of constant network issues. It was only a very specific set of circumstances which highlighted the phone was potentially at fault - and a change of device made night & day difference.
Genuine network issues do tend to be quite specific and localised. When phones are problematic over wider areas, the issue is usually closer to home than many users realise.
