Hi,
JoomSEF doesn't add any "Your SEO optimised title" to the page title, so please check whether some other plugin or component is causing this, or check whether your website hasn't been hacked.
In order to set the page title in JoomSEF, first you need to check the following settings in JoomSEF's Configuration on the Title and Meta Tags tab:
1. Enable Meta Tags management = Yes
2. Prefer JoomSEF titles = Yes
Then you can use JoomSEF's Meta Tags Manager where you can set the title for each SEF URL.