HIJACKED?? HACKED?? modem (internet /phone)

How is my neighbor accessing my modem (internet /phone) and listening in on phone calls? When my phone rings (very low) I hear him run downstairs and creep around outside my door, then he matches me step for step wherever I go in my house. I decided to reset my modem, and whenever I do I hear him scramble, run near my door, I hear soft clicking noises, then he goes out back on the porch and does something. I noticed that the circuit box (I assume) door for his unit is open when it is normally closed. What is he doing, how, and what can I do to stop it. ISP is no help at all.

 

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