You should be able to activate it here. You will have to do it from another phone and you will need a UK address. I used to have an Orange UK sim and I activated it from here.
Here is Voda's number:
Pay as you talk +44 7836 191 919
Vodafone Contact us
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile