|I'd begin to think that there is an issue with the phone system, modem or the ISP.|
Try looking connection speeds if it reports. Try a speed test site. I suspect it to be very low.
The most simple thing to do is to go outside (assumes you have USA phone) and remove the customer interface to your home. Wait an hour and re-connect. It is supposed to reset the phone systems devices.
You could connect there with the modem if you have a long enough cord or move all the stuff outside to bypass the house.
Look at the home wiring for any sign of damage or shorts. This is very easy to miss. Even a loose connection can cause all of this.
Borrow a laptop with a modem and try it just to rule out your side.
Might have to ask the phone company to run a tdr on the line.
Katy Perry, I'd never treat you badly.