My instalation was done improperly

My cable has been freezing up slow internet glitches with volume rewind , fast forward and simply enjoying my cable. The situation would always correct itself after about an hour. I was moving into a new home and work from home. The computer also affected my alarm system. Finally, I called and with hopes that they would take this into consideration. They sent a technician out and he said, my cable was never connected properly. From the beginning. They only want to refund me $40.02  That is ridiculous. My cable bill is $350 month. It's still not working properly and they're telling me that they can only credit me for the days after I called in. After clearly, the technician wrote in his notes that it has never worked properly. Why can't they execute proper customer service and  partially refund me from the time that it was incorrectly installed.?