Unstable internet connection and no one know how to fix it

I called customer service multiple times and the service agent also visited my home last week and replaced the modem. He checked all the wiring and confirmed that everything is fine but the problem is not fixed. The connection is not stable, wifi goes out multiple times a day, it works if I unplug the power and plug back in. Every time I call the customer care, your IVR does the same thing, restarting the modem as if I cannot do it myself at home. I called today to cancel my account and the agent transferred me to some retention department and it was outside of their work hours... phew... some customer care. Hope this reaches someone who can take care of the issue. I hate you guys for taking my money but not fixing the issue