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When using the sim does this mean within that period of 30 days you made calls, sent texts and used data which then helps the phones Imei latch to Vodafones systems.
If if not then please do try doing this for a few days and then try requesting it one more time. Don't keep trying or Vodafones systems will automatically pick it up as a possible fraud issue.
If you have then try inserting another Network active SIM card anyway and hook up to iTunes. Please see my tip below.
If you contact Customer Services via 191 and or Live Chat they can pass this onto their unlocking Nuc Resolutions Department and or supply you the relevant email address so you can contact them directly.
Tip > An iPhone is not unlocked via inputting an unlock code but instead is unlocked via Apple and their Database.
Vodafone would email you to confirm it's been requested after accepting your unlock request.
Apple then can take occasionally approximately up to 30 days to complete an unlock request made by a Network.
Periodically insert an active Non-Vodafone Sim Card in the iPhone and hook up to iTunes.
From the iPhone 5 onwards there's not normally the need to hook up to iTunes to complete the process.
You have to demonstrate that you are now the regular user of the phone. therefore you do need to make calls, send texts or use data at reasonably regular intervals over the 30-day period. Just putting a Vodafone SIM in, and leaving the phone switched on, but only making very few calls, may not create a sufficient record. I realise that this may be all that some regular users actually do with their phone, but you must understand that Vodafone has an obligation to ensure that you have a credible claim to be the regular user, so the bar is set a little higher.