As an existing M500 customer I signed up for an O2 SIM on the 26th of August, the O2 volt benefits straight through and the Volt benefits were applied 9 days ago.
Talking to a Virgin Media team member as the Broadband Boost hadn't been applied even though that was now 17 days ago via chat to be given the response below:
Hey Peter, I reviewed your account and I see that you are currently on M500meg broadband + stream with virgin media.
As you have separately purchased O2 you will not get the benefits of Volt.
The Volt benefits are been processed only when you are taking up a package of Volt + O2 through Virgin media.
This isn't mentioned anywhere in the Ts and Cs and seems to be them trying to wriggle out of a contract, one thing is for certain if they can't honour their own offers I won't be renewing ina couple of months when my contract runs out and will be moving back to Openreach.
This has now been resolved and the boost applied. I am still somewhat dissapointed that the boost had to abe applied manually following over an hour back and forth via Whatsapp and that I was incorrectly told it didn't apply to my account when it did!