Charged $500+ for an unintended international call

Hello, 

I am reaching out for help because I feel like leaving AT&T after this horrible experience after being an AT&T customer for over 20+ years.

This is what happened: 

• I went on a cruise out of the country from Apr 17- Apr 24, 2022 (from New York City to Bermuda and back)
• On the morning of Apr 17 (before I left home for the cruise terminal), I had to call this phone number 441-XXX-XXXX to sort out some covid vaccine documentation issues. I was on this call for 146 minutes but I spend about 2+ hours waiting in the queue so the actual conversation was only about 5-10minutes. 
• It turns out that the 441-XXX-XXXX number is an international Bermuda number but I had no idea because it was just like any other 10 digit phone number I dial in the United States - there is no way I would have known it was an international number. To my knowledge goes, to dial internationally, I have to first dial the country code, before the 10 digit phone number.
• I came back from the cruise and looked at my bill and I was charged $438 for that phone call + taxes (so my bill was $500+ higher than my normal bill) 
• I called ATT for help but the customer service rep told me that they had sent me a notification on Apr 18 for this abnormal activity, and that it was delivered and read. And because I didn't respond to that message, they cannot help take off the full charge. I DID NOT RECEIVE THIS MESSAGE BECAUSE MY PHONE IS ON AIRPLANE MODE from Apr 17 - Apr 24 to prevent international roaming charges. I double checked all my messages, voicemails, etc. and I DID NOT RECEIVE A MESSAGE FROM AT&T.
• The AT&T rep did reduce the charge to like $100 but this is still way more than what I can afford to pay. 

Please help! This is a very frustrating and disappointing experience with AT&T that I expect AT&T to fully resolve.