Huawei E5577C with EE sim no internet connection

[FlyingSkatesman]

Until yesterday I was using a Smarty SIM in my mifi device with no issue other than patchy network coverage.  Today I decided to buy a data-only EE SIM.  The mifi device will allow my phone to connect to it and use the internet, but absolutely nothing else.  I've tried with various IoT devices, Alexa, computer, and nothing sees an internet connection.  When the Smarty SIM was in the mifi device, EVERYTHING worked flawlessly, so I'm certain it's the EE network that's the issue.  I've spoken to tech support and they've really been rubbish "weeeell, since your phone does connect, teeeechnicallly it's working"... colour me furious! Any help or advice would be very much welcomed.  Tried rebooting everything, factory reset on the mifi device (which has good signal, so that's not the issue), and still no joy.

[XRaySpeX]

What is the router's Connection Status?

[FlyingSkatesman]

Connected

[FlyingSkatesman]

I think I've spotted something that *might* go some way to explaining the issue, might just be a red-herring though.  On checking Device Information with the Smarty SIM, there is an IPv4 WAN address and no IPv6 WAN address.  When I put the EE SIM in, there is an IPv6 WAN address, but no IPv4 address.  It's something that's different between the two.  How do I manage to get EE to assign an IPv4 WAN address?

[XRaySpeX]

It might be an EE IPv6 issue. EE has introduced IPv6 on its mobile network, but it doesn't fall-back to IPv4 nicely. Can you change the Profile/APN on your mobile router to APN Protocol = IPv4 only?

[FlyingSkatesman]

Only options I have for changing APN is User name, password and APN. Very limited options

[EssexBoyEE]

You cannot change or Edir an IPV APN Profile while it is currently in use, you need to set the APN to another Default Profile then edit it, or the easiest way is to create another profile with your preferences then set that as Default.