I’m very dissapointed with the customer service at the counter

First thiong I was asked, if I want upgrade, which I answered of course. I already prepaid everything for the car and then I found out that the amount for the upgrade was triple extra then I already payed. I refused everything and told the lady that I don’t want any upgrades just give me the car I booked. She got mad and said ok, I’ll give you the upgrade for the same amount. Everything in Italian on the invoice. When i came back to drop off, I found out that the same amount actually have to pay extra. And only way how can i Fight for my money is to issue customer complaint through web page. If I won’t resolve this issue, never ever again renting a car on Budget or Avis.