It sounds like the phone has temporarily lost it's connection @oliviareid , try completing a manual network scan from your connection settings, settings, connections, mobile network, manual, let the phone complete a scan, when it rejects the request reselect Vodafone.
Vodafone would recommend trying you SIM in an alternative phone if possible. If you continue to have problems you will need the phone and SIM checked, this is something that can be done through a Vodafone Store, if it turns out to be a phone fault, the store will be able to recommend a repair.
If you refer to device guides here: Device Guides you will be able to check SIM is inserted correctly.
