Over billed by xfinity

I traveled from korea and Philippines. I purchased a modem for home and travel service because xfinity gtp are not working  everyday! Very rare…. was told that Xfinity’s service would work while roaming and that the Global Travel Pass would protect me from excessive charges. During the trip, we turned off airplane mode and used our phones primarily for calls on my husband’s line. There was little or no usable internet connection in the area we visited, yet we were later billed almost $2,000 in roaming charges.When I contacted Xfinity customer service, I was informed that a refund would be issued and that a case had been opened under my account. Relying on these assurances, I continued using the service in good faith, believing the issue was being handled. Later, I discovered that there was no valid case number and no refund in process. This is unacceptable and feels deceptive. We deserves refund but all promises was only talks to delay tactic strategies