Only the carrier can legally unlock the device by issuing a Personal Unlock Key (PUK) and you need to ask them for it. They won't do so if the contract is still running or if there is money owing under that contract.
Pay up and they have to give it to you even if you have to see the contract period run out.
We don't allow discussion on the illegal way round this here in Tom's and anyone who posts it will be banned.