Could not activate mobile data network on Plusnet mobile

[hallb15]

I've been using plusnet mobile for several years without any issues with my iPhone 8.

Until a couple of weeks ago when I noticed that I was unable to use mobile data.

I can make/receive calls but no data. The phone shows 3G next to the plusnet logo on the top left, where it used to show 4G.

 

When I open an app that requires data it brings up the error "Could not activate mobile data network. Turn on mobile data or use Wi-Fi to access data."

 

It works fine when connected to WiFi.

 

I've tried various things based on recommendations from various google searches such as:

 

Removing and re-inserting the SIM.

Force restarting the iphone.

Resetting Network Settings.

Updating to iOS 15.7.

Erasing all content and restoring from backup.

Erasing all settings and setting up as a new phone.

 

None of the above has made any difference.

 

I was starting to think that there was something physically wrong with the phone when I tried my Wife's (SMARTY mobile) SIM in the phone and it worked straight away.

 

So I tried contacting Plusnet support who, although being pleasant to talk to, follow a limited script which leads them to say that the phone must be faulty, even though I can prove it works fine with a different provider's SIM.

 

I've run out of ideas so have ordered a Lyca mobile SIM to try. If it works, then great I get data back but I'd still like to know what the reason for it not working with Plusnet is...

 

Any edugeek ideas?