I assume you have a router? Connect directly to that with a network cable to your computer and do a couple of speed tests.
If it’s FIOS, that means it’s fiber optic into the house. Regular copper cable connections are prone to cause problems like these if they are not done right. Fiber tends to have better connections and less likely, but not immune to have the same problems.
You stated the cable was replaced. Is there an outdoor splice by where the cable was damaged? Splices can be a source of problems.
Did you try a router reset? Cable box reset? If wireless, an access point rest?