You could try going to the Phone app. On the first screen there, there will be a 3-dots menu icon top right. Tap that then there should be Settings. Tap that and you should get a submenu that includes Wifi Calling. If Vodafone have not enabled it on your account, the option will be greyed out. If VF have enabled it, you will be able to turn it on there. VF have been going through some accounts (particularly like mine) where users relied on a SureSignal. They are withdrawing SureSignal to be replaced by Wifi calling. 6 months ago I got a text saying Wifi calling had been activated on my account. Before that, the menu (as above) was greyed out. Not immediately, but a month or so after, the Wifi calling option was accessible. Surpisingly, VF have been making some improvements to their website Account pages, you might find a request option there, otherwise you may have to call them and suffer their "customer service"