Offered one price, signed up for another?

I recently contacted sales to get the price of internet for a new house I'll be moving into. The first time I called, I tried to get prices on internet packages and they quoted me 150 Mbps w/o free install for 64.99/month and 300 Mbps w/ free install for 69.99/month. The prices were to be good for 12 months. I even asked if the price difference was $5 and she confirmed.

I call a second time to actually set up service. I confirm with the new sales associate to get 300 Mbps for 69.99 w/ free install. She said yes, the price is correct and for 12 months. Things sound good so far.

I call a third time because I never really got any e-mail confirmation so just wanted to be sure the installation was scheduled. The person helping me says that I am scheduled for install for 300 Mbps at 84.99. Now I'm confused why I'm signed up for a price I've never heard of before. He says he can't do anything to change the price, I get sent to retention who also can't do anything. What is going on?

Is this normal practice to offer one price to get me to sign up and sign me up for a higher price without telling me? I had never heard the price 84.99 until I called back AFTER I was apparently signed up for the 84.99 price, making me think I was going to only pay 69.99. I'm glad I called back a third time before I get blindsided on my first bill, but why is this allowed? And no one can honor it even though it was offered to me TWICE until I finally pull the trigger on what I thought was a lower price? Can anyone explain what happened or how this can be resolved because it all sounds ridiculous to me.