international roaming charges - and false information

I recently traveled to Cuba and had inquired about international changes prior to my travel.  I was told that I did not need to do anything If I did not plan to use my phone while over there.  Unbeknownst to us that we were being charged roaming fees.  When we turned the phone on to hook to the in house Wi-Fi, we saw were we had incurred almost $400.00 in roaming fees.  Needless to say, these were not from calls we made to other people or back to the states.  I tried calling Xfinify while in Cuba and reach a person (twice) who did not speak any English.  I did reach an English speaking person who informed me that there was nothing that could be done on their end, but once I return to the states, to call Xfinity and they can remove the charges.  I was also told that my record would be updated to include the conversation.  I returned to the states, called Xfinity to resolve the issue and the nightmare began.  The 1st person said she could not reimburse the entire amount, but could credit me $100.00.  She advised that I call the Customer Support (CS) # at 888-936-4968 and they have the authority to remove all of the charges.  Prior to calling customer support, I visited local Xfinity store and explained what happened, they could not reverse the charges, but referred me CS and said they will remove the amount. 

When I called CS and they were rude, disrespectful, offered poor customer services, and made me feel like I was lying.  They claimed there was nothing recorded in my records of any past conversations I had with Xfinity and rudely said that I was trying to cheat the company of our money.  Taking into consideration,  I pay more for mobile and cable than I do any other bill in house outside of my mortgage.    How can I be a valued customer and be treated like [Edited: "Language"]....  They even refused to honor the 100.00 that had been previously offered.  

After reading the forum, I see I'm not the only one who has experienced this.  Had I known that I would have to pay this amount of money, and not have use my of my phone, I would have done things a little differently. Please advise what can be done to help in this situation.