Welcome to Vodafone Community
There has been an issue with the My Vodafone Application for part of today and that may be the reason the Application suddenly stopped working but My Vodafone is now back online.
If you have Vodafone Start on your applications, the My Vodafone Application will also be included and it may be an idea to uninstall and reinstall Start and download a fresh copy of the Application from there.
If you continue to have issues, please use live chat for account access, they will be able to get your application back online.
Usualky glitches like this self resolve.
Try turning the the phone Off and On to soft reboot it.
Which model of phone are you using ?
I ask because when an App is deleted on an android phone it's worthwhile then navigating into PlayStore, and pressing the little x next to the app to fully remove it.
Clearing App caches can help.
Clearing the System Cache can help.
If using an iPhone then navigate to iTunes on a Computer and remove it from the Apps section.
As a last resort backing up and Factory Reset.