Can iPhones be relocked by the carrier

So Xfinity was refusing to unlock my device on the basis I was not the first account holder to own the device, I eventually looked into it and the fcc states it should of been unlocked within 60 days of being paid off, and furthermore and that the restriction of me not being the original account holder didn’t seem to be defined by the FCC. I decided to do an FCC complaint and two days later got a call back from Xfinity where they unlocked the phone since it was on my Xfinity account. I have been using the phone with visible but I’m kinda worried could they reverse the unlock in the future?