Unless you use a separate and different 1) wireless password, 2) Base Station or device password, and 3) disk password, then it is very easy for anyone who can connect to your network to mess things up by changing names, and/or passwords around.....even copy or erase the data on the Time Capsule hard drive.
A real hacker would never change the name of your Time Capsule......because they want to get into your network without you ever knowing that they were ever there....and, they want to come back again and again to look for more data on your network without your knowledge. So, it is very likely that you already know who the potential "hacker" might be.
To solve your issue, you will need to start over again and set up the Time Capsule again with.....
1) A different name for the Time Capsule device or Base Station
2) A different password for the device or Base Station
3) A different name for the wireless network
4) A different password for the wireless network
5) A different disk password
Only give out the wireless password to those who you want to be able to connect to the wireless network.
Only give out the device or Base Station password to those who you want to allow to change the name and/or passwords on the Time Capsule using AirPort Utility
Only give out the disk password to those who you want to allow access to the Time Capsule hard drive. In addition, it is possible to encrypt your backups....if you are using Time Machine.....to further protect your data on the Time Capsule.
Unfortunately, it is still possible for anyone who has physical access to the Time Capsule to reset the settings on the device using a Soft Reset, so in some cases, users may need to locate the Time Capsule in a locked area.....if there are any devious folks around who might be tempted to change the settings on your Time Capsule.