Xfinity mobile- International Global Travel Pass - HOW DO I GET EFFECTIVE CUSTOMER SERVICE?????

We were traveling out of the country so my husband set us up on the Global travel pass prior to traveling. He called and verified that all three of our phones were set up for the Global Pass. He was assured everything was good. When we were at our destination, we had phone issues, he reached out to Xfinity. They helped us get online and assured us that the plan was set up on our accounts and to ignore any notifications telling us that we were use roaming charges.

When we returned home, once again, he reached out about the notifications we received and he was assured the bill would be corrected because we did everything correct and they were at fault.

However, nothing was corrected and we were billed $2,883.35! He called again, I called again.

EVERYONE we speak with say that we are not at fault, the company is and the bill will be corrected. Yet, no one on the phone can actually correct it. A ticket must be issued and an investigation will be launched. THIS NEVER HAPPENS. We have had 3 tickets issued, multiple customer service reps and managers telling us we will get a call about the progress. This has never happened. Instead of a $350 bill which is what we should owe, they will be deducting the erroneous $2,883.35 from my account. I'm furious that this isn't resolved. When we call, no one can actually do anything but issue a ticket. Where does this ticket go? Who investigates? 

What HORRIBLE "customer service". They have my account to deduct this money and I have no control. Disgusting. 

What are we supposed to do?