How to get a o2 unlock code

[AC Question]

My phone is locked to the o2 network and my contract is up and now my o2 sim is inactive. I changed to three but did not get an unlock code and now I can't call o2 for one on that number because it's inactive. Is there another way to get an unlock code?

 

[dov1978]

Ebay is usually pretty painless and cheap too.
I got an unlock code from there for an o2 locked phone I bought on Gumtree and it worked fine