Thank you for your query at DoctorSpring.com
I understand your concern.
It is possible that they injured the middle ear while cleaning the wax. Especially since they did it several times, the chances of middle ear injury is more.
I will advise you go to an ENT surgeon and get the middle ear examined first by an otoscope. The hissing sound will resolve, however, the chances of infections are high, hence it needs to be evaluated.
Feel free to discuss further,