There's no way to win with Vodafone really... Now is their SMS policy impacting on users' security and safety.
During the weekend I tried enabling 2FA on Twitter for a variety of accounts - unfortunately they use SMS authentication for this. None of the attempts to add a phone number to my accounts worked.
Today I tried again and managed to add a phone number to ten accounts and confirm this as 2FA - so in total received about 20 SMS... All seemed good and the 2FA even worked a couple of times - and stopped.
What I've heard is that Vodafone blocks some incoming SMS routes to prevent "spam" so I guess Twitter uses different routes, some work and some don't depending on how Vodafone sees these.
Lucky there's a single use backup code for these situations but ideally things would just work (on a more ideal world Twitter would switch to an authenticator app - it seems they removed this option though).