I suggest doing the tests by yourself and find out what's wrong.
from what I've read it's most likely a software problem. the test you can perform is:
connect a PC / laptop to your modem if you don't have one already (preferably with the cable)
open console (type cmd then enter in start menu) if you use windows
type: ping 4.2.2.4
and see of you receive replies from it

those mean you are connected to internet, getting replies from sun java company in NY and the problem is rooted in your OS/software.
It can be a range of things including changed browser or network settings to viruses and Trojans.
your internet company should've brought their own laptop and test this already.
hit me back with the result and I'll try to troubleshoot the problem. it's as easy as listing the possible causes and do a test to see if it's true.