Internet intermittently drops all day long

Since the docsis 3.1 update and a little before my internet has been very shotty it drops for up to a minute every 10-15 minutes sometimes with longer spacing ALL DAY LONG. This issue has rendered my internet almost useless I've had I believe 4 techs come look at it and 3 of them stated they noticed an issue that they fixed one even replacing my modem and router the (XB8) provided to me with my multi gig plan the fastest plan in my area. I've requested many times that the lines down stream from me be scanned and replaced as needed and one technician who came out told me that would happen but nothing no fix nothing. I spend far too much for this absolutely terrible service.