Welcome to Vodafone Community
If you are getting a server error your phone is not connected to the network make sure your phone has Vodafone UK at the top @Manchester123 .
Assuming everything is correct at account level. Try rebooting the phone and follow this with a network scan from your connection settings, connections > mobile networks > network operators > select manually - change this to manual and complete a scan > select any other network, wait for it to reject the request and reselect Vodafone. There is further support for your phone here: Device Guides
If you still have problems follow this thread complete the template and copy and paste and example of the issue for Vodafone to look at the network at your location here: Network Issues
Try a soft reboot by turning the phone Off and On please. Remove the sim card and gently wipe the chip on it. Re insert and try again.
Can I ask > Are you a new customer who's just ported to Vodafone UK from another network or an existing customer ?
If you've ported over please speak with Vodafone Customer Support / Vodafone Social Media Teams via Facebook Messenger or Twitter DM and ask them to check for a Split Port.
It'll be quicker asking Vodafone via Live Chat or via phone call.
Also as a process of elimination can you try your sim card in another phone and then see what happens please.
Current Phone >
Samsung Galaxy s²² Ultra 256gb Phantom Black.