completed WIFI extender exchange form multiple times, no reply fro Xfinity

I had a WIFI extender pod fail within 2 months.  I have completed the wifi exchange form 4 times, first in September and the last one in October.  I have not received any reply from Xfinity on any of these four occasions. Please tell me how I can return the failed unit for an exchange one.  Since Xfinity was so unresponsive, I had to go to the Xfinity store in Danbury CT. and purchase an additional one.  They would not take my failed unit and exchange it.