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yestday I topped up with £15 and already had £10 on my account so bought a £25 data pack which is not shown on my account and my my data balance is saying 0
When you purchase a data pack it will be queued, you are able to queue up to 5 packs at any time and each pack will start when the existing allowance has been used or at the end of the 90 day validity.
You will be able to see the queued packs from your dashboard or online account. There is further informaton for you here: How can I see my balance and remaining data allowance on my tablet, Mobile Wi-Fi device or Data Dong...
If the data pack is not showing on your account, the best way to get it solved is to contact Vodafone through the Customer Service channels for account access.