There are and they will reply in due course. I suspect that the problem might be that if you had an existing VM discount, that's been stopped, as Volt can't be combined with VM discounts. I'm not sure if that still applies to new customers on introductory discounts, but staff will be able to take a look and advise, if need be by private message.
It's not unreasonable to say that discounts and offered either can't be combined, or can only be combined in some limited permutations, and that's common with many other companies. But it is unreasonable, and a breach of consumer rights to offer and then implement a deal without being clear about the important terms. Small print can cover the detail, but the company can't rely on that to cover the principal terms, particularly when they mean a material change to existing terms which should have been clearly communicated. Even with the small print, on a quick scan I couldn't see in the T&Cs where they state that accepting Volt benefits will void any existing VM discount.
There are formal routes for ironing this out if VM won't play ball (forum staff, you'll know where that all leads), but wait and see what is advised.