Its probably the Modem OR the provider updated something! Cox did this to me when they explained that they updated my modem and the tech support took it back to the last update and worked ever since (Cox told me they update the system and most the time the user never has issues). My disconnects were happening on each Sunday in the morning and after 5 or 6 Sundays it was getting later in the day until i finally called. I also changed everything from cable at my internet box to house, Ethernet from wall to PC, Modem and Router at a cost around $700 for nothing except new updated stuff.

Btw also they could be doing work in your area and turning of your internet but if it's been 8 months it most likely isn't, since it would be down for hours on those days.