Data back online. So there was an action on the far end.
I had enquired with MG if there has been a contractual change, implementing limited data in the UK. Response:
"Let me clarify this. We haven't changed any contract items on this. We did not provide unlimited data before. So, may I ask who informed you that the data was unlimited? [...] If we have any new change of the data plan we will let customers know. But currently the data is limited to 1 GB per month. There is no way to increase the data amount now. We are internally working on a better strategy on the data limit now because we also received same complaints from other users. Thank you."
Strangely enough I can connect to the hotspot now, but don't get Internet connection through it on my cell phone. This has never happened before. Weird.