WhatsApp failing to connect

[Anjistar]

Sorry to bother you, I posted this on the forum but it got rejected by the moderator.

I'm tearing my hair out here. Very suddenly, but while our local O2 mast was down, WhatsApp on my galaxy s10 stopped working. It notifies me that I may have new messages, that's all.

Before that, WhatsApp would always switch to mobile data at home, although we have FTTH, and if I check the WiFi when the message comes up (WhatsApp is using mobile data because the Internet connection is not reliable) it's running fine, at least 525mbps, and all other apps also work. 

Strangely, WhatsApp works fine on my WiFi-only galaxy S7 tablet and on my Windows laptop. So it must be something to do with the phone. 

I have tried ALL the suggested options to be found online, apart from getting O2 to check my APN, which I will do today.

[MI5]

@Anjistar 

If you go into your network settings and reset them it will automatically apply the correct apn. 

[Cleoriff]

@Anjistar 
advice from Whatsapp

Fixing issues on WhatsApp

1. Check your connection. Make sure you have a good internet connection. ...
2. Update WhatsApp. Make sure you're updated to the latest version of WhatsApp on Google Play for Android and the Apple App Store for iPhone.
3. Turn your device off and on again. ...
4. Close WhatsApp and reopen it. ...
5. Free up storage space.

[Anjistar]

Thank you,  I've already tried all those things. 

I contacted What's App support but they insist it's a phone problem, not an app issue,  and now won't reply at all.

[Anjistar]

Thank you. I did that, sadly to no effect.