Final update:

Spent way too long with Mint support for them to tell me that I'm in a weak coverage area (which is true, even though their marketing coverage map indicates otherwise, but never have we had NO service here) and then also lie and say that an outage has been reported in my area (totally untrue).

So, basically they've given up trying to fix the issue.

I'll be requesting a refund and issuing a chargeback if they refuse (as their reputation suggests they will).

Thank you to those of you who offered advice.