Internet disconnects all day every day every 30 min or so

I have been having the issue for the last 2-3 months I have had a technician come out gone through 3 different modems all ones provided by Xfinity, About every 30 mins I have a connection interruption where all my devices disconnect, and say no internet connection. I have used the app texting service to speak with people and talked on the phone for hours and have not had any progress in fixing the issue. When the technician came over they checked all my signals and said that it shouldn't be a device issue but some issue at Xfinity and their system 

At this point, I have no faith in Xfinity to take care of any of their customers as the whole time I have been having these issues they have had no problem with continuing to charge me every month with no issue.