VM have recently started pre-activating their equipment, and the box should call "home" and be activated within 30 minutes, however sometimes this fails and the advice is to sign into Check Service Status at the top of this page and run a test against the TV box you are installing. By doing this we’ll be able to reboot the box or put you in touch with the right team.
The old method which you tried still works ( calling 0800 953 9500 ) however if it's not being picked up then you could also try contacting New accounts and Set Up for them to complete the setup and activation. That would be options 1,1,1 and 4 if dialling 150 from a Virgin landline , or options 1,1,2 and 4 if dialling 0345 4541111 from any other phone. Unfortunately as you've seen it takes patience
You could try the freephone number 0800 052 0422 instead of the 0345 number if those numbers aren't included in your call plan.
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali