First, take a deep breath . . . Good. Now let's fix your problem.
Understanding how the settings on your panel work is a huge part of server security. I'll quickly review each feature as it pertains to the security of your server.
Under your "General" tab you have the option to toggle your settings between "private" and "public". This allows you to control who is allowed on your server at any given time.
Your "Whitelist" tab allows you to add other people's usernames and is a type of safe list. It would be wise to only add your most trusted MCPE friends to this list as it gives them the power enter the server at any time; even when you're not playing.
The "Ban list" tab lets you add people's usernames who are trolling you by destroying your world, attacking you or your friends, etc. These people will no longer have access to your server. Basically, they're banished!
Last, you have your "Ops" tab. When adding a friend's username to this list use extreme caution as they will have as much control and power over the server as you do. Thereby making it possible for them to ban you and your friends! These people can change passwords, mimic your username, and allow their own friends onto your server. So be careful!
Now, what if you have been banned, or someone continues to troll or ban you? Submit a ticket and we can get you a new password if you need one. Then, when you have a clean start I suggest a couple of things:
1. Enable SimpleAuth. It can be time consuming to put in your pin each time, but probably less so than dealing with trollers.
2. Change your settings from "public" to "private".
3. Be careful about who you Whitelist and even MORE selective about who you Op
4. Don't give out your personal information about your server over public entities such as forums, blogs, social media, etc. Chances are you'll get a ton of traffic from a bunch of people who haven't had to work to build your trust.
Good luck! Be safe! Have fun!