Hi
Can you clarify whether your wanting to send normal network text messages that send in a green bubble or iMessages which only send to other iPhone users that show in a blue bubble and require a data connection.
If normal texts make sure you have enough texts left in any allowance and check your Vodaphone masts are ok via
https://www.vodafone.co.uk/our-network-and-coverage/uk-coverage-map/If iMessages then try deactivating the service in the iPhone's settings and re connect. Official  link here
https://support.apple.com/en-gb/HT201287 And
https://support.apple.com/en-gb/HT201422Your iPhone has a facility to block calls and texts too so it's worth checking you have not accidentally added a person and ask that the person your texting to check they haven't added you.
 official link on blocking a number to stop calls and a separate one to stop texts is
https://support.apple.com/en-gb/HT201229Try resetting your iPhone via On the iPhone hold down the Sleep/Wake Button and Home button together until the Apple Logo shows. Then On seeing this Apple Logo release both buttons ,and the iPhone will reset , which has been known to clear most glitches.
Other options are :
Settings -> General -> Reset -> Reset Network Settings.
If this fail then As process of elimination can U try ure Sim in another phone2 rule out either the Sim/Phone which may be at fault.
If your sim does not send texts in another phone then speak to Vodaphone Customer Services via phone or Live Chat via the 'Contact Us ' link at the foot of the forum page.
Good luck.
😎
Current Phone >
Samsung Galaxy s²³ Ultra 512gb Phantom Black.