The Wi-Fi speed you are getting is pretty good. Wi-Fi can be affected by tens of different outside influences including building construction, other electronic devices, neighbouring Wi-Fi and smart appliances - the list goes on and on.
Wireless is easily disrupted by a number of external factors (Thickness of walls and building materials used within them, mirrors, fish tanks, cordless phones, baby monitors, microwave ovens, a neighbour's wireless router, etc.) so it is not something VM can control or guarantee.
Also not all wireless devices will be capable of 512Mbps. Only my Samsung Galaxy S10e maxes out my 350Mbps connection with most of my wireless devices only getting 200Mbps or less. What devices are you testing on?
If the bottleneck is not your devices then you could look at getting a third party router to improve wireless speeds with the VM hub in modem mode.
My setup: V6 TV box, M350 Fibre broadband with Hub 3 in modem mode connected to a Netgear R7000 router. Telewest/VM user since 2001.
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