Overcharged for MultiChoice System Incompetencies

I called DSTV contact centre to request a mere decoder swap ( Primary decoder to be changed to secondary) which was done swiftly BUT somehow affected my monthly bill of which is senseless as I am on a price lock. When I called again 5 minutes later I was told “Sorry that’s how the system works” I am being charged extra for calling and asking Dstv to provide a renaming/reallocating service of their decoders??? Where is the fairness in that?? What happened to my price lock? Clearly there’s a problem in your systems BUT why is it affecting me as a paying customer. These were questions I asked the contact centre agent and all he could say is “Sorry it’s the system” moreover the team leader refused to assist with my query let alone take my call. Please help!!!!!