Pathetic service from Cell C

Every second month there is a problem with my debit order, I notice that has not gone off on time even though the money is available. I pay Cell C, send them proof of payment and phone in to say that the debit order has not gone however the consultant tells me it has, doesn't matter what I say. Then at a later stage they still try to debit my account and because the debit order then returns I get penalised. I am sick and tired of having to pay an extra R70 every time this happens. I will never recommend Cell C to anyone. Just run when you hear their name. I also wanted to cancel my debit order, however they also don't allow that?