Very Rude and disrespectful Agents who harass me at work

On daily basis I keep getting calls from different agents whom I have asked on multiple occasions to call me on my mobile number which I've handed out each time since they always claim not to have. And today I received a call from this rude agent by the name of Sithembile who was so rude and disrespectful towards me and as I was about to get the reference no for the call she than decided to hang up. I than called them back with the hope of reporting her behaviour to her line manager and I was told that she does not work there and that there had no one by the that name and that they did not have a line manager by a lady who introduced her self as Hlomula what an acceptable behaviour with very poor customer service.