Hi there
There are several settings to disable the permission. If your old fb account still exists you need to go to the fb "settings", then choose "apps", there you see the Township button with a cross beneath you have to click to delete. If you use fb via the safari browser as well as via the fb app you have to do this on both if you are logged in with both. Additionally you may need to go to your phone settings to undescribe from some more permissions, one of it is to log out facebook in the main menu.
BUT there also is an easier way: You can deinstall the Township app and then reinstall, so ALL facebook connecting settings are deleted wherever they are active so far.
For this you first need to
ensure you are logged in with your Game Center account! (with which you usually backup and sync games).
Notice: If you had been logged in the Game Center so far, means you used to back up your game via the Game Center, you can deinstall the Township app immediately.
If you didn't use the game Center so far, means, you only backed up your game via facebook, you first have to activate your Game Center in your device settings and then do any action in your Town so Game Center saves your game.
Now you can deinstall the Township app, then go to the Appstore and reinstall the App. After reinstalling go to Township, click the red field to connect to facebook and the game will ask you for your account.
Good luck; if you need more assistance you are welcome to ask
Addendum: Oopsi, I have been slow, didn't see Lea before I finished 
Addendum 2: To change your forum name you need to contact the forum admin Anastasia Bukina, she is the only one who can do this.