floof.org
This just smells so scammy. But they have the planned activation date and the second half of the postcode correct, and the phone number matches one on openreach's web site, so… presumably it's genuine?
I think it's a "proceed with extreme caution" situation.
They sent a grumpy followup message saying, basically, "okay, well, I suppose you didn't really *have* to reply and we'll assign the port to you anyway" and giving a link to a comms.openreach.co.uk URL which I'm quite happy to follow, which basically just says to make sure the ONT is present, plugged in, switched on and has a sane configuration of indicator lights on it, which it is and has. All good.
I just had another thought: the messages were from what looks like a normal mobile number, but perhaps it's actually a "special" number that costs more to message. If so, that would be why it failed; I have no credit on my giffgaff account, only my monthly goodybag (although it seems they no longer call them that, huh), which is a good protection against scam messages from expensive numbers trying to get you to reply without realising.
Just to be clear, your service provider has almost certainly *not* asked Openreach to contact you on their behalf.
They will probably ask you to trust pilot review you later as well. Maybe put that in the review, and how scummy it looks.