Yes, please tell everyone you know to avoid 3 at all costs. The tarrifs may appear cheaper, but you pay for it in the end!
It took me 45 minutes on the phone the other day to get them to cancel my contract, I had already the operator that the reason for canceling was because 'I do not use the phone anymore' - I repeated this about 3 times, he eventually asked 'please give me your reason for leaving, other than that you do not use the phone' so I said I had another commitment to another network. At this point I was put on hold at one point for 15 minutes while the guy supposeadly cancelled the contract.
When he came back on the line he said he had spoken to his manager and realised that I had bought my phone from a 3 store, so go back to a 3 store and they will give you a new phone and a new contract(?), I now said 'I no longer wish to discuss this, cancel the contract now'. It took another 15 minutes still before he was able to cancel the account. I have since called back to check that he really did cancel, as I had no confidence at all in his abilities.
I cannot offer any advice to you for how to get the PUK code, only to be VERY patient and persistent and ask if there is any other method for verifying the ownership of the phone (maybe throught the simcard number and the IMEI number of the phone?).