SIM APN Problem?

I have a sim which I've just moved from a Glocalme Numen, dumped because the battery swelled, into a new Glocalme MeowGo G50 Max.  It's worked fine in the Numen for a few years.  I'm now not getting internet access.  The device is connecting and I can see that the sim is there and the signal is fine.  It loaded APN settings for 3, which I assume came automatically or what was used in the previous device, it loads with an APN type of dun but it won't accept that saying "Carrier does not allow adding APNs of type mms, dun, etc."  so I tried to set the APN using the Smarty recommended settings of Internet+MMS which it accepts but them but still no luck.