Wrong date debit order which resulted in unpaid charge

I took out a new contract with Cell C 2 months ago. From the beginning everything was a mess. I gave the consultant my banking details and he captured Capitec bank under STD acc number. I called in since no debit went off then the error was rectified and i was supposed to be debited o the 20th as per the initial agreement. So now i get a returned debit on the 17th Nov where Cell C tried to debit. I called in to collections and spoke to a rude Lesego Mosiua(not sure of surname spelling) who was busy doing her other things and after confirming my details and couldnt answer why cell c tried to debit on the 17th, she hung up on me. Now i'm sitting with a returned debit on my profile & a charge of R115. I want to cancel my contract and never ever want to deal with cell c. Pathetic behaviour from Lesego.