Nokia 515 access control code

[Justiier]

Im trying to insert a new pay monthly card to a Nokia 515 which shouldn't be restricted to any network, however the phone is asking for access control code when I first start it. How do I get that code please? 

[Justiier]

Edit: I'm trying to insert a Vodafone pay monthly card. The phone used to have a pay as you go O2 card but wasn't originally bought in any network. 

[BandOfBrothers]

The only reason that the phone wouldn't accept a Vodafone sim card is if the phone was locked to o2 @Justiier 

Where was the phone originally purchased from ?

And or the sim cards sim pin has been activated which is a security feature to stop the sim being used in any unknown phone without inputting the 4 digit pin.

[Justiier]

Thank you for your response. The phone was bought from Carephone Warehouse and paid for in cash without an operator. It was meant to be simlock free hence why I don't understand why it would be locked to any network..

It's the first time I've tried to use the Vodafone card, is it possible that it's already secured with a pin code?