If you can't access your Facebook or Instagram account, try resetting your password using the 'Forgot password?' link on the login screen.
If you no longer have access to the associated email, visit facebook.com/login/identify and follow the instructions to prove your identity and reset your password.
If your account was hacked, visit facebook.com/hacked or instagram.com/hacked/ on a previously used device and follow the instructions provided.
After regaining access, change your password to something strong, enable two-step verification, turn on 'unrecognised login' alerts, remove suspicious friends, and consider advanced protection options.