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I would like to know if it's possible to request to see the content of text messages from a particular number that is appearing on my bill?
Text messages are not stored on the network. Vodafone would be unable to see the content of any message.
Some back up options also back up text messages. You could check that @MsMackers
I'd not then even a subject to access request to Vodafone costing £10 wouldn't help as the networks don't have access to the actual content of text messages.
Not being nosey but can you request a duplicate copy of the text from the sender of the text ?
Are these premium rate texts? If so, there are bars that can be added to your account. There are various ways to get them stopped, too, but you may need to contact the originator if you can't see anything on your phone. Be careful with this as you may be giving additional information to a scammer, but some are reasonably legitimate services that you may have signed up to, possibly unwittingly.