Well there is always the option of leaving VM for another supplier.
You know what I find curious is the number of posts on here asking for ‘upstream and downstream stats’ or have been fixated on RFoG specs, even though the OP has stated that “The speed to the hub is 1gb, just over, the ethernet speed is also full speed, it's just the WiFi speed which has gone down since the upgrade”. So assuming we accept their claim that they work in IT and know how this all works, and they aren’t just lying, then can we please work on the basic that the underlying connection is fine and that this is a WiFi issue?
So how do we investigate WiFi only issues? Now the OP claims that nothing else (other than a speed upgrade) has changed? How do they know? WiFi is no respecter of boundaries, hypothetically, I could move into the next door property and install equipment which would utterly obliterate my neighbours’ WiFi connections - from their perspective ‘nothing has changed’.
So, again ‘how do we start to investigate WiFi issues- get a grip?'