Modem upgrade saga

Due to us buying a 4k TV and new AVR receiver we wanted to make sure our internet and TV settop box were the latest. Ours were both ~4 years old. The cable modem was an ARRIS.  We called the 800 # and were advised to get a new XB6 moden and 4k DVR. Off we drove to the Comcast store! I went in, explained my intent, he scanned the incoming, outgoing, put them in a bag - done. When I got home I saw that the two new items were the same models as I turned in. What? To add insult to injury the 800 # tech we called then spent an hour trying to convince us that this equipment was "compatible" with our new TV.  Luckily we hung up with her, called the 800 # again and got a great agent. He told us to go back to the store and insist on the new XB cube modem and sleek 4K DVR. We got them, they work great. But we wasted a whole afternoon! Ugh.  Check what they hand you at the store! Don't let them just smile and stick stuff in the bag.