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You have been sold a new contract with a new number, that usually happens when going through a third party.
Unfortunately, that means having to cancel your previous contract and transferring the number to your new contract.
The quickest way to transfer the number to your new contract is to ask Vodafone for a PAC for your previous number, port out of Vodafone on PAYG to any other network, request a further PAC and port back into Vodafone on the previous number. The other way is to transfer the original number to PAYG and transfer the number to the new contract, the problem going this route is with 30 days notice this is going to take 30 days to complete.
If you upgraded through Vodafone, this is done through your online account, by calling telesales or through a Vodafone Store, this would have enabled you to upgrade the same number.
Please see this link to keep your number: How can I keep my mobile phone number?
Who did you upgrade via @millie09072005
If you have a cooling off period I'd use it and then start again instead of messing around with transferring stuff.
That said it's your choice.
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You will need to speak to Vodafone through the Customer Service channels for quickness, you only have 14 days to cancel.
Not sure the reason for Vodafone providing an extra line against your account, Customer Services will be able to help.
Alternatively, you can wait for the forum team to catch up with the thread but it won't be quick when time is limited.
This is going to need account access, contact Vodafone as soon as possible through the Customer Service channels, they will be able to access your account and find out what has happened.
You don't want to be stuck with having to pay 2 contracts and will need to get the original contract cancelled by following the procedure in my first reply and the number transferred to your new contract.
Really don't understand the reason for Vodafone providing a new number. Customer Services will help.
On the same account, I have a relatives phone so that the monthly pay is easier, will asking vodaphone to cancel the contract of my old phone affect this?
I use the vodaphone app to keep track of my bills etc, for efficiency reasons, my relative also has their phone linked to the same vodaphone account, and so each month my relatives phone, and my phone are paid as one bill, but my old phone is still on the bill.
Having had a further thought about this it sounds like you have taken out a new contract through my offers and not an upgrade.
It also looks like your relative may be the account holder for your previous contract and your relative would need to do the upgrade.
The easiest way to get this sorted is to start again and providing you are still in the the 14 day time limit by cancelling the new contract and this may need to be done by your relative as the account holder.
The other way is to ask your relative to do a change of ownership for the previous contract, but your relative will need to do the upgrade first before the transfer to you or you won't be able to upgrade until the third payment has cleared. Further information here: Transfer number and agreement
Fortunately, you still have your old phone but will need to set this up again using the SIM with that contract.