Possibly the cause is over-utilisation, in which case VM often close off complaints because there's nothing they can or will do, since there's more data traffic than the local equipment can handle, but it is expensive and difficult to increase capacity and rarely gives positive returns on investment. As over-utilisation is invariably a self inflicted injury for VM by virtue of selling more contracts in an area than they have the capacity to support, they are sometimes (not always) very cagey about admitting to these issues. I believe VM had a telling off from Ofcom a few years back about this, and promised to make sure they aren't selling contracts that the equipment can't deliver, in practice whatever checks are in place aren't always working.
You confirm (or deny) if this is the case by visiting Thinkbroadband.com creating an account and setting up a Broadband Quality Monitor. Let that run for 24-48 hours and then publish a link back here. If it doesn't show the normal over-utilisation fingerprint, it may still offer some insight into the extent and possible causes of your problem. If it does show over-utilisation, then its time to start thinking about a different ISP, because the normal "fix" is to wait for sufficient customers to leave in order to bring the local network back within its capacity, and this can take months, and occasionally years.
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