Mediumship, psychic readings, and fortune telling are not the same things.
Mediumship is communication with spirit, via a medium. The purpose of it (according to the Spiritualists National Union) is not to predict the future, it is proof of survival - e.g. when the medium gives several pieces of information such as names, accurate descriptions of the person (including their appearance, character, names, interests, what caused them to pass, their occupation etc) or specific details - usually it is small but specific details that give the best proof. It can, and does, give people comfort and guidance. Some information about future events may be given, but predictions should be avoided (if the medium is sticking hard and fast to SNU rules), though they often do.
Psychic readings, which can also use tarot cards or other 'tools' (e.g. crystal balls), are where the psychic reads another person. There is no spirit contact with a psychic reading. Regarding predicting the future, sometimes guidance can be given, but generally it's more about giving insight into where someone is at right now and their path forward and what may or may not influence it.
Fortune telling is specifically about predicting the future - generally where people will end up in life, in the long term.