Most terms of a cease and desist letter are usually reasonable.
When you receive a copyright infringement notice, usually the copyright holder will simply ask you to "cease and desist" use of the copyright. If one’s ISP has sent a copyright infringement notice, then either their technology has detected infringing activity (usually based on visits to torrent sites and the like) or the copyright holder has sued the infringer, claiming someone has used the ISP’s network to download content illegally. A notice was sent to your ISP identifying the particular infringement and the associated IP address.
The infringement notice you received is the result of your computer having been identified as engaged in an illegal transfer of copyrighted music. If you have a copyright, sometimes you have to enforce it against those infringing on it. Your reply can be as simple as informing them you have removed the infringing content or a receipt from Shutterstock attesting to the license to use an image. Whether you determine that copyright infringement exists or you can prove that you had permission or the work is yours, reply to the notice.
When you’ve created something that’s one-of-a-kind, you want to make sure it stays that way. For instance, scammers piggybacking on the HBO Game of Thrones IP-Echelon copyright infringement sent thousands of scam emails including a direct settlement fee of $150 for the alleged copyright infraction. Some copyright infringement notices also contain a notice of payment, causing people to panic and pay without considering if the letter is real. Do not ignore the copyright infringement notice.