Hello there, Without the information requested in my first/previous response, I can only give you a general answer, but I hope this helps.
If you can't unlock the parental lock, then the only option to fix is factory-reset it. Factory reset will erase everything from it and return it to new (like Out of Box). This is how they designed the device. So first backup all your important files to your computer or online. Let me know if you need instructions to do that.
Follow the steps below to factory reset it
Open Settings > Backup and Reset > Reset and factory data reset.
If that didn't work, then try the steps below. Make sure you follow the steps below exactly or it will not work;
Turn off the tablet.
Press and hold down Volume Up and Power buttons at the same time.
When it turns on, release the Power button but continue holding down the Volume Up button.
Android system recovery will be loaded now (may take up to 2 minutes. Press Volume Up and Power if it shows No Command)
Select wipe data/factory reset.(Volume buttons to go up or down, select with Power button)
Select Yes — delete all user data.(Volume buttons to go up or down, select with Power button)
Then select reboot system now(Volume buttons to go up or down, select with Power button)
That should factory reset the tablet.
After the factory reset, you need to set up the tablet again (like a new tablet). If there is a backup made on Samsung or Google account, you will get your data back.
If you are unable to reset it from there, then try to erase it from this site (make sure you erase this problem Tab and not any other devices) --> https://google.com/android/find
(Login with the same Google account you used on the Tab to erase it)
If you have any difficulty following the steps above, please let me know and I will walk you through it.
Please note, I can only give you truthful information which you may or may not like but it is truthful information to your question. If you are upset at your situation but not by the quality of my answer, please consider rerating positively as I am only a messenger. If you simply want more information or continued help, please let me know - I am here to help you to your satisfaction. If you have other concerns, reply and let me know. I am here to make sure you are satisfied.