The SIM that you currently have inserted in this iPhone is from a service provider that is not supported under the activation policy that is currently assigned by the activation server.

Only the carrier it is locked to can unlock it. Neither Apple nor CPW can unlock it.

You need to go back to Vodafone and tell them its still locked to them, and they need to unlock it.

If they have already unlocked it, you may need to restore the iPhone to factory settings to complete the unlock process.

click here ➜ How to unlock your iPhone for use with a different carrier - Apple Support

I believe the ban applies to phones sold by the networks themselves starting in 2021. i.e Vodafone cannot sell a phone that is locked to itself since then. Phones sold before then have no such restriction.

However CPW is not a network, and does not directly sell locked phones. It mostly sells phones that can be activated with any U.K. carrier, but lock to the first carrier used. The legislation on that subject may be broad enough to let CPW do this.

There you go then. In that case, there's not much that can be done. Its locked to Vodafone and they won't unlock it for you, because you did not buy it form them. That is their very specific restriction.

Though it does make one wonder why they would say it's already unlocked, if they don't unlock devices not bought from them. They should know it was not bought from them, and would have said they could not unlock it, rather than sending you to contact Apple or CarPhone Warehouse, neither of which an unlock it.

https://forum.vodafone.co.uk/t5/Unlocking/Nightmare-unlocking-an-old-iphone-purchased-at-Carphone/td-p/2675342

You need to work it out with Vodafone. Only the can unlock it. If they are not willing to do this, then there's simply no way to unlock it.