Ford Fiesta "or similar" and I get a I20

For our engagement I organized with Avis to rent a car for two days. I was told that I might not get the Ford Fiesta if it is booked out, but I will get something similar.

This I am fine with, so I will get a car with the same horse power, luxury or space. When arriving there, I was told I can get the I20 and when asked how this is similar I didn't get any answer. Not to make a scene on the big day I decided to just take this.

Walking through the parking lot I could find any ford fiestas, not on the day I received the car and not on the day returning. This seems very strange.

I emailed Avis numerous times with no clarification on how a I20 and a Ford fiesta is the same. Horse power lacking, not the same size and definitely not the same luxury. Not to bad mouth the I20, but I paid for something else. There is also an option to hire the I20 which is cheaper but I couldn't get my money refunded for the difference.

Next time I will book the I20, pay less and who knows, maby they give me a BMW because it is "similar"