Internet dropping constantly

My internet has been dropping constantly over 8 months. My modem have been charged out about 7 times. I added and extender because the tech said it would correct the the problem but it didn't. I have had 8 or 9 tech come to fix the problem most of said I can't do nothing because it working but I will change your equipment out to see if that help. If time I call in the person on the other end assured me me once I put in your they would stop until the problem  was solved and time it was a lie. So I ask one simple question how do I get in touch with the corporate office, they still haven't gave me a answer as to date. Instead of during that, they put in for yet another tech to come and lie to me. In have been going on over 8 months if they won't fix on there own maybe corporate can light a fire. Send relief please.