Welcome to Android Central! Belodion is right. Passwords on your phone are extremely important to remember, so if you're prone to forgetting these things, try writing them on a piece of paper and keeping it somewhere secure (like a home safe).
Im having the same problem on a j7 prime. Forgotten pin . and main screen when phone turns on says that the phone has been encrypted enter pin. Only its CRUCIAL that I dont loose any info.. Samsung and metro not helping