That's a positive response from MG, at least for the short/medium term.
It was me who presumed my Live Services data had run out for the month. I'd been using Amazon Music a fair bit, so thought it was possible.
I started a supermarket trip from home, then after a short while tried accessing Amazon Music, as usual.
Was presented with the Amazon Music welcome screen (select the Amazon country, etc). On choosing amazon.co.uk, the webpage sign-in screen did not display - got Android error: DNS Cannot Resolve Service Name.
Then tried Sat Nav, instead of operating as usual it displayed the welcome screen, with the "Get Started" button greyed out.
Checked Infotainment software version in case it somehow updated over-the-air, but still at R29.
On enabling a wifi hotspot on my phone and connecting to it from the car, both Amazon Music and Sat Nav resumed working (with Amazon Music, it automatically signed-in, didn't need to re-authenticate)
Surprisingly, on next journey after quick run round Tesco, and mobile hotspot turned off, both services continued to work on MG built-in SIM data.
Point to note - when the iSmart data services (Amazon Music, Connected SatNav) were not functioning, I was still able to connect to the "core" services on the car over mobile data. So I was able to view charge status and so on from MG app.
I was in good mobile reception areas at all times.
The MG iSmart app also signed me out - perhaps the car system / MG mobile provider / MG API gateway had gremlins?