You can go to Samsung's FindMyPhone and log in with your Samsung account. From there you can unlock the device (it will also reset your device's password). This only works if you didn't disable Remote Controls and are logged in with your Samsung account on the device (and have a valid network connection, of course).
Unfortunately that's what a secure lockscreen does: secure the device. If you don't remember the right credentials, there's not much you can do, unfortunately.
A carrier service station might be able to factory-reset it but you'll have to provide proof of purchase.