Internet Never Works

Since moving into my place in Sonoma in July 2020, technitians have come out to the house multiple times to fix the service and all leave baffled.  The service randomly starts to work for a few days or a month and then fails again.  I have to call and then they send a technician will advise me that I have the right working model, the signal at the house is great, and the signal from the junction box to the modem is also great.  What is the deal here?