International roaming charges

Hello! Was unaware of being charged for the international roaming. Simultaneously I asked for Unlimited plan and thought that I could use my phone overseas. At the end, my bill went up to $600's. I asked agents to help me out to waiver it or to lower the bill. They gave me a ticket and then in a few minutes I got a text where they cancelled my ticket. I have been an Xfinity mobile and Comcast client for 5 years having 5 lines and paying for both services over $330 each month. And I felt disrespected the way they cancelled my ticket and didn't try to help. What happened to long time client forgiveness and willingness to help?