Did you set it yourself after setting up your Google account. Was it encrypted, or does the company have Administration rights.
Try Google's Android Device Manager from a pc with your Google account as the S3m won't be on Android Lollipop. Set a new lock and should override the old one. As long as Android Device Manager is still enabled in Security - Device Administrators.
Google are making this lock override obsolete on new Android versions, (this wasn't it's primary purpose) and you would need to remember your original lock with Android 5.0+ so it seems.