Well ill start this the best i know how. My friend is having some major internet issues and no matter how many times he calls windstream and they "FIX" it he still has the issues. i have tried to help him but know i dont know everything so i figured i would jump on here and see if someone with more experience could help. The first problem is that when ever someone connects to his wifi his internet just goes to complete shit. he cant play any games while someones on because of how much lag there is. Second his internet will sometimes just go to complete shit regarless if someone is on the wifi. this usually happens at night. He has called and tried multiple time to get windstream to fix these issues and every time he does it goes away for a week or two then comes right back. also no he cant switch he's internet. where he lives windstream is the only internet provider. i also had them at one time and know how shit they are specially there customer service dont know shit about the internet or how it works and have on multiple time cut him off while he is talking or just hung-up on him. Also from what i know about he's setup is a modem/ wireless router combo. also yes he's computer is connect via ethernet cable.
Sounds annoying. Some questions.
What brand and model is the modem / router?
What does windstream do to "fix" it? Try to get them to explain it in an email. If that won't do because customer service doesn't know what they are talking about, then try to sweet talk a mechanic into explaining (if one is ever visiting to come "fix" the issue).
Does the problem persist across devices? Are you absolutely sure that his computer is not the problem?