very angry customer and feels betrayed

goodday i am not sure if this is the correct platform to complain to, concerning bad service i have recently got a contract with mondo telephonically so basically the sim was delivered to me however they delivered two sim and i cancelled one the day after because i did not sign up for two.i am honestly frustrated because now i am being billed for two sim.when i called in natalia gave me a wrong case number then shortly after i called in again after talking to telkom billing crew who advised me about the case number being in correct i then called mondo again who then said the cancelation was sent today which doesnt make sense cause the cancelation should have been done before the 7th of august if i am not mistaken.my problem now is that two sim will be debited on my account without my approval.please help