Bad service

I upgraded a line on my account in November 2014 on a u choose smart L package it was on this line in January we wanted to load a data voucher and could not I contacted Vodacom to inform them of the problem and they told me that the contract is an open contract I told them that that is not the option I chose and that they need to correct it.I also told them that I will not be laiable for an account as I did not choose an open account, they have billed me R2500 for an account that should have been R960, I have spend about 20 hours on the phone, I have 8 service requests in I have spoken to consultants, supervisors (Deneo Matswalede) and Manager (Ntuli) they promised me that they will phone me back, I am still waiting for a call it has been 6 weeks and in total almost 20 hours that I have spent to get this resolved, I get promised that they will call me back with answers but to no avail, this is atterly discusting how they treat clients I don't know how supervisors/teammates can be appointed if they can not sort out a problem. I am so disappointed and disgusted with the service I got from Vodacom. I can not be kept liable for there incompetency.