Salvador, what steps have you taken to voice & document your complaint:
(a) To the operator - who not only has duties under aviation legislation but also has Health & Safety duties & rsponsibilities to his/her employees & customers. penalty last time I heard was £20,000 + jail sentence.
(b) To your instructor - who as an employee has the same as (a)
(c) To the engineers - who as sub-contractors have ditto
(d) To the CAA.
Is the defect noted in the flight log for the school? How much discussion has gone on regarding this?
There are good channels to work through to get this sorted.
Be careful in getting at the operator in this public way if you have not taken all reasonable, documented steps to rectify it yourself - if you are a member of a club you may even have a (legal) personal responsibility if you have not documented your concerns to the appropriate club/school people and authorities.
Hope it gets sorted!