Special Offers is a feature on Fire tablets. Apparently you opted in when you got your Amazon device at a discount. If you opt out you will charged whatever your discount was. If you still would like to remove it follow these steps.
1. Sign in to your Amazon account, and go to Your Account > Content and Devices > Devices.
2. Select the Kindle device from which you wish to remove ads.
3. Look for a line that says Special Offers. ...
4. Click the Remove offers button, and follow the instructions.