Dishonest service

Has anyone been lied to about their service? I had switched to ATT and was going to cancel Cox. When I called to do so, I was offered a deal (gigablast and unlimited data for $90 per month) to retain my loyalty. The data was very important to me as we are home schooling and I work from home due to my wife going through chemo and the risks of Covid to her. I accepted. Fast forward one month and I am getting hit with data overage charges. I called to have the issue corrected (mistakes happen, I understand) but was told that they would not honor what I was originally told. I asked if they could listen to the original conversation and hear that I was promised the unlimited data as well. They said they are not able to listen and that only the quality department was. I asked to be transferred there and they said that I am not allowed to talk with that department. Convenient. They promised me one thing, I cancelled my previous service based on that promise, then they did not deliver. When I offer an option to prove what I was promised, they were unwilling to cooperate. What good is a quality department if they have no idea if the representative is lying or not and are unwilling to investigate to do so? I am hoping a representative reads this and is able to help me out as no one on the phone seems to care. I only want what I was promised......