MTN DISHNONEST TOWARDS ME

My name is Thandeka Masuku I entered in a contract with Mtn for a chromebook for a period of 24 month the initial amount was 320 but they would deduct 780 , 500 sometimes 480 and now went beyond to tell that I am on a.36 month contract which I have never agreed on . I have called their call center and asked for Masingita who was helping and who also added these extra month but everyone claimed that they don't know him and couldn't atleast reevaluate the value and asisst me . I have lost hope now since my last payment was suppose to be in September 2023 but they are still deducting