Excessive Roaming

This seems to be a recurring issue for Xfinity customers. Upon arrival at my overseas destination on September 2nd, I purchased a local SIM for data. Despite this I was still charged for data usage. An agent removed the charges, confirmed my roaming was disabled, and ensured me that I would no longer receive charges. Upon returning to the US on October 19th, I see a bill for over $13,000. I did not receive any notifications to bring awareness to these charges. As another user also noted, Xfinity states online that they would terminate roaming if charges became excessive. $13,000+ apparently is not deemed to be excessive. 

This style of business comes across as predatory and an attempt at intimidating customers into paying these exorbitant fees or risking damage to their credit. I am requesting a review of all charges to be sent to me privately so that I can dispute them and clear this bill.