Maybe you have never been frozen before. GOOD try to keep it that way. BUT this guide will definitely help if you ever befall an "accident." First thing you want to do on your UNFROZEN account is to go to the support page via the Help page at the bottom of neopets.
After finding that link you will then find the link saying request support and then submit a ticket. Find where it says Frozen Accounts in the Issue Type section. Now here is where you really need to be specific. Read each input selection carefully.