I was having no end of problems with VM, but I got a new(er) model router and that sorted a lot of things and then I actually downgraded my bandwidth - they wanted the deal I had been on for years gone, and gave me a choice of what to move to, and I went for the cheapest one that i thought would fit my needs - and since then it’s been pretty much perfectly solid apart form the general wobble they had that Dan refers to.
I suspect people are signing up for the 200MB/s deal when in fact the local cabling etc. they have actually can’t reliably support it. But they don’t seem to do any ‘we’ve checked your line and it can support X’ with customers, just say ‘you can have our new top speed!’. I suspect they care more about getting customers locked into a 12 month contract than they do the actual customer experience.
personally, I am keeping an eye on 5G home broadband options. In theory they’ll be really competitive both technically and in terms of price, and I will finally be able to not have a landline and pay line rental any more.