Since he doesn't teach well, tell him that he wants to change teachers. You paid for it.
You are like a boss who is afraid of firing his employees. You know that employee's skills are poor and can't bring any benefits to the company, but you support him and keep giving him opportunities to continue to fool him.
If you really can't talk, or you can tell him: I have other things to deal with recently, so I can't go to the tutor class. For example, attend cram schools for other subjects, or take a summer job or something. It is said that there is a conflict in time, so there is no way to leave. Then finally I added, when I am busy, we will contact again to discuss the future tutorial (if not, he will pester you to ask when to continue his tutorial).
You can tell him that your parents have invited another teacher to be your tutor. Because there's no way to reach him or anything. Said to teach him next time.