PUK Code Problem

So my SIM card is locked. When I go to unlock it by entering my PUK code, I type it in, and then it asks for a new code. So I type in the new code, and it asks me to confirm it. And after I confirm it, it says "Incorrect PUK".

Example: Enter PUK Code: 1234, Enter New Code: 5678, Confirm Code: 5678, Incorrect PUK

So how can I fix this?