Untrained call centre staff

Called 808 to query out of bundle data charges on my account as I purchase a bundle as soon as I receive the SMS advising that my bundle has been depleted. Grace advised that it is not possible to load additional bundles onto an open line. I disagreed and this argument continued until I asked to speak to a manager. Grace said that she would see if 'someone was available' to speak to me and that I only wanted to speak to a manager because I was unhappy with the information she giving me. A manager was unable to speak with me - a second argument ensued between Grace and myself. I once again asked to speak to a manager. I was placed on hold for ages before Grace came back and told me that she must 'refrain' from her last comment and, that it was indeed possible to load a bundle on an open line. I do not use data out of bundle, yet I have been billed R 750 for out of bundle charges. Please can someone call me ASAP to resolve this. I am not willing to deal with yet another untrained call centre agent.