The main problem is that you are only seeing one end of the connection. You know you send protocol 41 packets, and you would be receiving them if any arrived, but you don't know what's stopping things or where.
And I can't quite make sense of that reply from Netgear
and it is somewhat contradicted by Netgear's own product data sheet.
There are still other things you can try. Presumably the netgear is connected to the VDSL2 modem so you could try bypassing that if you have a laptop and pppoe software on it, disconnect the netgear and connect the laptop directly to the modem, start pppoe and then set up the tunnel - see if it in this case (I would expect it does!) and that would at least tell you it's not BT infinity blocking it (I can't imagine why they would, but you never know). Of course, you'll want to do this test quickly as the laptop would be fully on the internet without the protection provided by a firewall.
I can think of other things to try too, with increasing level of difficulty to set up, so I wouldn't try to say anything here unless it's necessary...