According to this link Trade In , the time limit is 14 days of your airtime agreement to return the phone for trade in.
Vodafone would have sent a returns pack with a prepaid DPD label to your address for you to take to a DPD collection point where you would have scanned a QR code and the return would be tracked. I wouldn't be surprised if DPD return all the Trade ins in one go rather than individually.
Vodafone will have the return logged in the system as it would have been when you scanned the return and you probably won't have anything to be concerned about. When the phone is accessed by Trade in you should hear something shortly after the 7th October.
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