That's disappointing to hear. If you're the account holder then it should just be a matter of passing initial security checks then an authorised contact can be added to an account. As you've not been able to resolve this with customer services, you can escalate the issue here.
In terms of accessing texts sent to a data SIM, most routers and Mifi devices do have an SMS/text inbox if you log in to the device using a browser on another device. Typically using a process like this:
Enter your device's default gateway IP address in the address bar. Most devices will use the default router address 192.168.8.1, 192.168.1.1 or 192.168.0.1.
Enter your router's username and password, then tap Login. The default login credentials can be found on the back of the router.
Once logged in check if you have a messages or SMS section in the admin pages. Failing this, our data SIMs should also work in a phone too if receiving a text is necessary for some reason.
I will note that our Broadband teams would usually default to sending security codes to the account email instead though, so it usually wouldn't be necessary to take these sorts of steps.
Thanks,
Jonathan
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