Like many VM customers, I too need all my future invoices to be VAT invoices. I've been trying to find a way of contacting VM account support but the website keeps directing me to none relevent and unhelpful advice without giving up a means of contacting VM directly.
Thanks for your message. Please don't just PM, it needs to be a public message first then on to PM if need be.
I have checked and it's more than likely your bill was produced immediately after the flag was added thus too late for it to make an impact on this current bill and should be fine for the December bill when that's created.