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I have travelled from india to UK with my Vodafone SIM card which was from india and I recharged for international pack but still I don't see any network bars on my phone.
First a Warm Welcome to the UK.
Try turning your phone Off and then back On.
Is this happening in one place or everywhere ? If in one place them maybe the local masts are at issue.
If you have another phone then as a process of elimination try your sim card in that one.
Vodafone India and Vodafone UK are not linked I'm afraid, so the Vodafone Uk Social Media Team's or Vodafone Uk Customer Services cannot access your account unfortunately or help you with this.
This is the Vodafone Community Forum for UK Customers.
Therefore if your myvodafone app or online myvodafone shows roaming as available and your phone's settings does not have any relevant settings in connection to roaming you need to toggle On, then I'd first suggest to go into your phone's settings and then connections and see if there are relevant networks that Vodafone India partner with in the UK and choose one.
If that does not help then perhaps contact your Vodafone India Customer services / Social Media Team's to have your account checked.
If all else fails and if your phone is unlocked to all Network's you could consider using a local Network Sim Card in the interim while your in the UK and or make use of any available Wi-Fi.
Current Phone >
Samsung Z Fold³ 5G.
Previous Phone >
Samsung Note 20 Ultra 5G - SM9860.