Old Account Information --- How do I get Xfinity to Flush It?

When I moved a year ago, the "transfer service" facility did not work.  I won't go into all the problems that had to be fixed, but it took several trips to the brick and mortar, long chats with humans, but finally we were able to establish service in our new house.  The problem is that Xfinity still has records of the old account, and that data has a bad habit of popping up when I try to add a new device or service.  The most recent example was a Roku TV, which for some reason kept loading my Xfinity account info from the old, deactivated account.  The Xfinity Streaming App would not load properly; that prevented me from accessing all Xfinity TV services, so I returned the TV.  So here is the question: how do I once and for all flush that old data out of the Xfinity universe?