iPhone 13 locked can't use eSIM card

Just wanted to vent. I was told by Xfinity and by Airalo that because my phone is locked, I can't download an eSIM card. I know other people who have eSIM cards but either their phones must be unlocked or different carriers. Anyway, last year in Europe, Xfinity charged me $10 per day for their global plan. Just outrageous to come home and have $150 tacked on to my phone bill. Some days I might have used the phone for 5 minutes. And this is not for talking, just looking up stuff on the internet while I'm out and about. My phone is not paid for yet so no chance of unlocking. I'm so put off by this!