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Try turning the phone Off and On.
Van you try your SIM card in another phone as a process of elimination to rule out the phone or SIM card.
Try manually choosing another network and then rechoose Vodafone if you can which refreshes network connection.
Does this happen everywhere.
Check that there is no inbuilt data bar in the phone and that there are no caps set in your myvodafone and that you have enough data left to use.
Customer services on 191 or Live Chat can access your account and check things from there side.
Current Phone > Samsung Note 9 _512Gb > Model: SM-N960 Hybrid-Duos.
Samsung Gear s3 Frontier Watch.
may not be the same thing as what happened here two of our handsets data stopped working what we had to do is turn ON the data Bar leave 10 mins then turn OFF the data bar wait 10 mins then re start the phone number we then had the data working again after the restart