Welcome to Vodafone Community
The criteria for unlocking is the phone has to have been used on the Vodafone network and the phone has not been reported as lost or stolen.
You can get round using a PAYG SIM by asking your employer to get the phone unlocked, although the number is cancelled , Vodafone should still have details of the IMEI registered to your employers account.
The only other way is using a PAYG SIM but all that should be needed is to make a couple of chargeable activities to associate the IMEI with the SIM, you shouldn't have to wait 30 days now.
You probably have the link: Unlocking
The 30 day usage stipulation has been removed so you'll just need to use the sim card in the iPhone for a short while to make a few calls, texts etc so that the iPhones imei latches to the new Vodafone Payg account,
Now Vodafone have two criteria.
1. The phone was bought directly from them.
2. The phone hasn't been blacklisted.
The other option is to use a Highstreet Store that advertises they unlock phones for a fee or use a reputable online unlocking site that's also reputable, although they'll charge a fee too.
In regards to unlocking an iPhone via Vodafone.
As an iPhone isn't unlocked via a Nuc but instead is released by Apple from its database after being requested by Vodafone this can sometimes take longer , sometimes upto 30 days which can be longer than a phone that uses a Nuc.
I wish you all the best with this situation.
Current Phone >
Samsung Galaxy s²² Ultra 256gb.
Secondary Phone >
Samsung Z Fold³ 256gb.