Billing error, I was charged for something I was told by an agent I would NOT be charged for, cannot reach live person

I was chatting with an agent and they told me I would NOT be charged for a technician to come to my apartment to find my cable outlet. But my next bill has a $100 technician charge on there. I have a screenshot of the conversation between the agent and I, and she said the technician will come help me with my issue at no cost. I can't get anyone on the phone to resolve this. This is so upsetting, I'm about to go into a store and cancel my services. Someone please assist.