Not saying it is or isn’t in this case, but most speed issues can be found in the home; poor connection where the cable meets the house, poor connection at the master socket, incorrectly filtered lines, or even radio interference from cheap electronics messing with the Wi-Fi.
Also turning off a broadband router regularly will fool the exchange into thinking there’s errors on the line. The automatic equipment in the exchange will lower your speed since lower speeds are meant to be more reliable.