Didn't honor rebat that sales rep stated

My wife and I went to Best Buy to look into DirecTV.  My parents had the service and told us that we could get a $100 rebate for them and us if we used them as a referral.  We mentioned this to the Sales Lady and she told us that we would deal with that with DirecTV when we had our service.  We asked her again if we needed to do this first, and she confirmed again that we do it after.  We signed up and before we left we again confirmed that we need to do the referral after we are installed  After almost a month bit was finally installed.  Four days later we called to  get the rebate, and we were told that we were supposed to do this before we sign up.  We called and talked to a sales rep and he told us they couldn't fix it.  A manage also told us the same thing.  The next day my wife called and after talking to four different people, no one was able to help us.  This is all because their sales rep told us the wrong thing.  They messed up and we get punished.  After having the service for four days were already regret our decision and are stuck for 2 years with it.