HTC One - How to unlock a One S?

[CasualCoquette]

Hi there,

So I got a phone on kijiji from someone whose plan had run out. The number now doesn't contact the phone, no data, etc. It's basically a wifi device right now. I want to put my current number and phone provider (Koodo) onto the phone. I have a Koodo SIM card, but my issue is that the phone is still locked into the Bell network. Since I'm not the account holder and now can't get the original owner to contact me, how do I go about getting the phone unlocked? Bell won't do it since the account isn't in my name. I know there are third party systems but I have no idea which to trust, etc.

Any advice?
Anyone else who has unlocked their phone?

Thanks!