To disconnect, you have to open a terminal and type

sudo poff dsl-provider

If you want to connect again, type

sudo pon dsl-provider

What I do is I have saved the first command in a text file named connect.sh and kept it on the desktop.
When I want to connect, I double click on it, and then choose “run in terminal.” It prompts me for the password in the terminal, and then connects.

Same can be done for disconnecting.