I had to once get the PUK code for my mom's phone (she doesn't have Cricket but I'm pretty sure it's similar) and it was a pain in the butt. You have to call customer service and tell them what your situation is and that you need a PUK code.
Your PUK code is usually the last four digits of your phone number. However, if you have changed it and forgotten the code it is possible to get around this...
Reset your puk code by pressing *228 which will take you through the activation process. From there you will be able to reset your PUK code so it will again be the last four digits of your phone number.
Alternatively, you can talk to the network and ask for their help. If you go to the website https://www.cricketwireless.com/ there is a live chat option at the top of the page.
If you prefer to talk to someone on the phone, their number is 1-800-CRICKET (274-2538) or 611 from your phone. You can call between 7am and midnight ET.
I hope that helps, cell phones are amazing but so frustrating when there is a problem.