PUK number not working

I have bought O2 sim card (prepaid) couple of weeks ago. The SIM card is working fine, i.e. calls, internet and messages. But when I am trying to register to the O2 app using my phone number, the app is showing that the PUK number is invalid. I entered the code exactly as per the SIM packaging and even tried PUK2. Note that even though the PUK is not working, the PIN given in the packaging is working perfectly fine. I am currently unable to view remaining balance.