If this is a recent-ish problem, then it is very, very likely to be over-utilisation on account of home working, schooling, and higher leisure use of the internet. Over-utilisation is when the amount of traffic local to you exceeds the capacity of VM's equipment at the top of the coax network. Whilst for chronic problems VM will invest to increase the capacity, they do that rather too slowly for most customers' satisfaction, and they don't provide accurate and open information about when and if it will be fixed. But for a probably Covid-related over-utilisation fault, I'll stick my neck out and say that they won't fix any of those. There's quite a lot of these issues at the moment, I suspect it's rather embarrassing for VM, but if it were your network, would you spend the couple of months technical planning effort and possibly considerable sums of money to resolve each problem you hope will be sorted by (guessing) April?
There can be other causes, such as issues with your household network, or capacity or routing issues for the gaming or video-call servers, but if you setup a BQM over at https://www.thinkbroadband.com/broadband/monitoring/quality that'll show what's going on with your VM connection. Post a link to a live, shared graph here and we'll see what's happening. Usually needs to run for 24 hours before we can draw reasonable conclusions, but the live graph will continuously update so you can do that immediately.
If this is over-utilisation and it's recent, then assuming you want to keep the VM speed and and other package elements, you'll just have to sit it out. You could take your business to an Openreach ISP, but install times will be highly variable - if it's just reconnecting an existing socket to an available tap in the cabinet, then that might be a ten day job. If it requires a technician and work at your place, that may have a two month lead time. Obviously you'd need to be out of a fixed term contract with VM otherwise there's exit penalties, and you'd need to do your research to make sure you'd be happy with the speed and service you'd get elsewhere.
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