Sometimes it will be the same toll-free number that you would call to make an order; sometimes it will be a separate "customer service" number. Look around on the back cover and the order form.  Call the university recruitment office and cancel the flyers. Whether you're a prospective student or you've long since graduated, these recruitment materials can be a pain. The best way to stop them is by calling the university recruitment office and requesting it be cancelled. If you are a high school student already getting recruitment literature from universities, ask your counselor to help set things straight for you. Occasionally, the customer service people will ask why you want to be removed. Simply explain that you are not interested in the products offered or that you're not planning on attending this university. Be kind, but firm. Have the catalog, or at least the mailing label from it handy when you call. Often they will request a tracking number or other code printed there. Many catalog and mail-order companies offer opt-outs on their websites. If you prefer the convenience of a web form, look around the catalog or the company's website and you will often find one. Many schools get your information when you take the PSAT, SAT, ACT, or other standardized test. When you sign up for such standardized tests, read the form carefully. Likewise, many mail-order businesses, especially printing houses that print checks and personalized stationery, often send other mail and sell the addresses of their customers. Read carefully when filling out any form to make sure you're not agreeing to receive catalogs. CollegeBoard, the organization behind the PSAT, SAT, and AP tests, states that their "Student Search Service" program is voluntary [1]. ACT states in their privacy policy that you have a choice of whether to receive communications in excess of the required ones.

How would you rephrase that briefly using Chinese?
致电个别商品目录公司或试图招生的大学，让他们把你从邮寄清单中去除。 准备一个回复说辞。 在网站上退出。 在寄送之前就阻止他们。