Cut internet cable

It does have protection. It has 1 layer of plastic sheathing, 1 layer of dielectric and several layers of metal shielding. See here for info. However none of that can protect again a tree falling on it or a animal chewing through it. To prevent that, it would have to armor the wire so much that it wouldn't be economical and would weigh too much. Some areas bury the coax underground to further protect it, but then you are affected by water in the ground and people hitting the wire when they are digging for something else. Long story short, stuff happens. 

Did you end up figuring out what took down your line?

In Europe we put cables inside plastic tubbings, I don’t think that is expensive. My guess an animal chewed on it.

Isn't most wiring in Europe underground? If so, it would be in conduit like it is here. Whether wiring is above ground or underground depends on where you live and isn't controlled by the ISP. 

PS. Getting zoning permission to lay wiring underground is probably the most complicated and expensive part of installing new infrastructure. It's what keeps many ISP from competing with other ISP. 

The answer to your question is, the wiring from the Demarcation point, (Where the Cox cable comes up to the home) forward into the home is the homeowners responsibility for repairs. The cable coming UP to the home is Cox's responsibility. 

That being said, Cox has a service called Cox Complete care which is 10$ a month will cover the repairs. 

https://www.cox.com/residential/support/cox-complete-care.html