It works for some and not others - never has for me either !
It always best to do this on the phone as thats where you can get the best deals. Its more difficult at the moment but is still working.
Call in -- 08.00 sharp is the best time. People are still reporting getting through ok. Go to “Retentions” on 150 or 0345 454 1111 - options 1-1-4-4- "Thinking of leaving" when you have the best chance of getting through to the only still open (UK) call centre. They are the people who can help you.
Also, another number has been posted openly which may help in this regard.
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.