Download Speeds Dropping Every Few Hours

My broadband connection is driving me insane. My download speeds keep on dropping to sub-5mbps across all of my devices, every few hours.  Upload speeds are completely normal and unaffected by this. 

When I turn my Hub 5 off and on again, my speeds return to normal, but then a few hours later, it happens again. I’ve run all the service checks, I’ve had my hub reset etc. but the same thing keeps happening. 

I go through the help process and they reset my hub for me, which again, appears to fix the issue, so they consider the issue resolved on their end and close the case, but of course, the speeds then drop again a few hours later and I have to go through the whole process all over again. 

i started having this issue issue about 6 months ago, and it persisted for about 3 months, but then it stopped happening, for no apparent reason and went back to normal. Now, 6 months later, it’s started happening again. There are no reported service issues in my area.  My best guess is the hub, but whatever it is, I’m at wits end with it, and I’m fed up of the web chat never working!