No upgrade

On Friday 27 October 2017 I visited a Cell C store at balfour Park Mall. I had been due for an upgrade. I was kindly assisted by a gentleman by the name of Ntembeko. We processed everything and when we were just about to finalize the upgrade he told me that they were out of stock regarding the phone I wanted. He asked me if he could order it for me and that I would surely have it on Monday. I was okay with that. On Monday he surely did call to say my phone was ready for collection. I went to the store on Monday 30 October 2017 to finalize my upgrade and collect the phone. I then signed a few documents and he says that he has to make one last call before we're done. Once he's done with the call he tells me that my account has been closed and I can't upgrade. I asked what was the reason for that. He told me that there were two occasions that my account was debited late due to insufficient funds in my bank account. Yes that is true but for both times I have explained that the fault was with the bank and not that there was no money for the debit orders. I'm very unhappy because I have been a loyal customer with Cell C for over 10 years. For both times that the bank had made a blunder I called to explain what had happened. Why is it difficult to upgrade now? What about all the times I have paid for my contract?for you to close my account based on something that I had no control over? Why couldn't they call the bank? I don't like the way Cell C has handled this matter and I will have to cancel both contracts I have with them and find myself another service provider.