I have had the same problem with two of my Samsung Devices, my Tablet and Note 4 phone. After changing my PIN (to a number I absolutely KNOW is the same), it denied me access. With my phone, I tried the device manager but it would tell me that it was "Google has determined that a device lock screen password is already set". and would not gain access to the phone. I ended up having to do a hard reset. Now the same message has come up on my tablet. Is there another way?