Well, to follow up, I took the advice of the moderator and rang Telstra Nbl support. After being on hold for 27 minutes, I spoke to an operator who started looking into it. As it was morning, the speeds were ok but variable, 22 to 33 Mbps, rather than night where it drops to 1 to 5 Mbps. I believe she was speaking to a tech person, then muttered I will look into it further.. If there actually a problem.. And call you back.
As you can guess, never did, and there is a problem otherwise I would not be taking the time to ring and sit on hold for 27 minutes. The issue still exists, but I really don't want to sit on the phone again for that long, not to get anywhere. Can someone suggest any other way that someone can actually help, that does not involve me taking up more of my own time and apparently wasting it?