I don't know my PUK number, i can't make or receive calls, it says 'locked SIM' instead of my carrier, and i don't know what to do. Please help

So i woke up this morning and entered my passcode to see that i needed to enter my PUK number i had no idea what that meant. I soon realized that instead of my phone saying 'Sprint' in the top left corner, it says 'Locked SIM' after i tried googling what happened, and it wouldn't let me, unless i turned my wifi on. Everywhere i looked it told me to call my carrier, and i tried but everytime i try to call, it says 'Called Failed' and the call ends. I can't call anyone, nor can i receive calls. Please help.