Hey there. I’m a 1K flyer on UA and have been in your situation only 1 time, so I’m afraid these things happens, but it’s really rare with equipment change like this. You were probably on an A fare, discounted First Class.

If you write UA a nice e-mail telling them you didn’t get the product you paid for, they will give you a refund (most likely UA travel vouchers) for the leg you had to fly economy. (I would guess around USD 250, but no promises…)

I’m sad you didn’t get to try the E170, it’s a great commuter aircraft!