I wouldn't say an engineer visit is the "stock answer" to calling in, but it is the correct answer when there's no recognised fault and remote diagnostics fail to resolve an issue. In that instance, "boots on the ground" is the best fix.
Equally - the VM staff on this board should have visibility of your account notes, so can probably tell what's been tried already here and what the next step is. I don't have that luxury, but it sounds potentially like a cable re-pull could be needed. This is where the drop-cable from your home to streetcab needs replacing, and unfortunately - for various reasons - this is not always a quick process.
Personally, I think the complaints process is useless for progressing this - that's good for service-related issues, but this is a fault that needs resolving. If nothing else, complaints come with a 28day SLA which when your fault is live and affecting service, that's no good.
It's also possible that 1) Your fault needs escalating within VM Networks, and somehow, that is falling between the cracks, or 2) You have multiple faults, each of which only get identified when the previous one is cleared.
If you wait around here for a day or so, VM staff should pick this thread up and hopefully give the necessary "kick up the rear"..
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