How do I file a complaint regarding a corporate store employee?

My son and I went to upgrade our phones in our local AT&T store.  We were told of the BOGO on the iPhone.  The employee told us that in order to get that one of us would have to get a new number.  We did not want to do that, so he then said they had a deal on an iPad for $99 and we would just have to pay $10/mo for service on it.  He said the iPad would get my son's old number and his new phone would have the new line.  Then, he said we could swap the cards/numbers and my son could have his number back.  We did that.  Then, our first bill came.  Of course, the guy lied to us.  Even the guy on the chat said the sales people lie to increase their commission.  He did not tell us that due to having a 2-year contract on the iPad the other number would not be eligible for the $25 discount on the monthly access fee as it was not on the NEXT plan.  Well, my bill in print says I am on the NEXT plan, so somebody else is lying.  If we had known all that, we would have paid full price for the dang phone instead of the BOGO as it would have been cheaper for us.  I have literally spent hours and hours on chats trying to clear this up.  I spent 3.5 hours on a chat just today to basically be told they could not give me what I was promised.  I then had to cancel my iPad contract to get out of that for $150.  However, in order for my son to keep his number, I still have to pay $10/mo on the line THAT IS NOT USABLE as we had to cancel the iPad on that line.  Somehow, my son's phone installments are attached to the new line.  So, I now pay $10/mo for access fee for that nonexistent line and $15/mo for my son's access fee.  When I walked out of the store, I was going to be paying that exact amount but WITH the iPad having service.  Now, my iPad has no service AND I am out $150 for canceling that.  It is unbelievable that one of your employees can lie to me and nobody can do anything to rectify that.  It is also crazy that it is this difficult to find a way to file a complaint.  I need a way to contact someone to do something about this.