Welcome to Vodafone Community
I've had a similar issue; I've bought an iphone 7 from CEX and want to use non-Vodafone SIM in it. I can't afford to not receive calls for 30-days whilst I have a PAYG SIM in it with another number so need to get it unlocked now.
Just like you, I have got no where with getting Vodafone to unlock my phone.
Their process is too complicated.
its expensive to contact them.
their staff are not equipped to resolve issues.
You have to grease their palm at each disfunctional stage.
the process does not work presumably because they have not unlocked it.
After this, In what remains of my life, I will not have further contact with these useless people.
Ahhhhhhhhh My phone is still not unlocked.