Sputtering connection

my internet connection is sputtering (disconnecting every 3 minutes or so and then quickly reconnecting). Speed test i.e. Showing 180Mps to 200mps. No problem with the speed, just the reliability. Problem listening to spotifY as it stops every song or two or when my son is playing playing online and he's already near the final level then it will loss connection. I have two routers, one provided by cox which is 600n, and when they connected it, the technicians saw that I have a 1900ac router. 3times faster so they let me use it. I tried disconnecting the 1900ac router just to test, it's still doing it. By the way, my Spotify music are already downloaded to my player so its should be a lot easier to play but it is not. And also currently I have used just 8% of my 1000 GB data plan. What could be the problem?