That is crazy. You are being disconnected and reconnected multiple times. Stupid question, but did you ever try using another modem router, and another cable? Just remove everything on your current network and use a different modem router, and a different cable, and see if that changes things.

Sad to hear that. There must be an issue with your line. There is probably degradation somewhere.

It must be a site-wide issue then, and they might have botched the installation of the physical infrastructure. Your only hope is that they start laying new fiber infra and decommission the current copper cables.