So this has been going on for about a month now. I do a factory reset on the router, and the speed is fine - about 40mb/s. Not bad and what I should be getting.
However, after about 5 minutes this drops down to about 0.3 to 2mb/s and stays there until a reset it again. I have tried different channels, and on multiple different devices, but the problem persists. I refuse to call the ironically named helpline again. Last time I called them I was sat on the phone for an hour, with the conclusion from TalkTalk being "We'll send a technician round.... That will cost you £65."
My housemate has a Virgin fibre connection and gets 150mb/s.... I feel like such an idiot for sticking with TalkTalk.
From what I've seen, A LOT of people have this issue with the HG633.
I'm not paying for my service for this month, or until this is fixed by TalkTalk at their expense. I've not been able to use the service I pay for, so why should I pay for it.