Internet goes out. Customer service issues.

My internet keeps going out.  I have done the reset/troubleshooting 20+ times.  Technicians have been here twice and both have said they made repairs. The last one replaced the modem. I have contacted Xfinity no less than 11 times regarding this. Yesterday an agent promised me a credit and a tech appointment. Neither happened.  Last week an agent promised me a $40 credit.  I received $4. Today I again made an appointment for a technician.  I am beyond frustrated. How do I get this repaired permanently.