Hi Elshaar,
Sorry to hear you're having a frustrating time with your internet connection.
It can be very hard to know what the issue is after it leaves your router/modem. I would ask for a technician to come out and check the line from your house to the pole/box to make sure it's not on your premise. After that, it's up to them to fix it as it could be a DSLAM, a bad cable, or a host of other things.
Here is a good
article on how to build a solid case to bring to your ISP. Remember, the squeaky wheel gets the grease and just keep asking to speak to a supervisor until someone who can help you is on the other end of the phone.
Good luck and let us know how it goes!
Thanks,
-Poe