Billing issue

Our internet was out all of June and after contacting ATT several times to send a new modem, it was never mailed to us. They are trying to charge me $63 for that months internet service, when we never had internet. I have a screenshot saved of an ATT representative telling me in a chat that he will waive that for me. It was never done. I also talked with a phone representative who promised to waive it and it was never done. What do I do now?