Hi @TillyFloss welcome to the community your post has been flagged for assistance and you should hear shortly.
Let me suggest the non techie solutions!
Disconnect the router from the power supply and go for a 30 minute walk. Halfway round disconnect your phone.
When you get home reconnect the router, shortly after reconnect the phone.
Then send me a message saying that was a waste of time:-)
But at least we tried!
Hi @TillyFloss well you wanted the non techie solution, what it could do is cause your router to return to operating correctly and allow WhatsApp to work.
If you want we can try to get you into the router admin page find the DNS settings fiddle about with them and then still have to wait till Monday for a response from the excellent OCE team who only work office hours. Enjoy your weekend I'm off down the pub.