comcast/ xfinity poor cable service, multiple appointment, some no shows, some incompetent,customer service- uneducated,cable box keeps freezing internet has low signal why? 6 months?? southestern Pennsylvania

i have had xfinity box from comcast for  6 months.  there have been problems since we got it. glitches freezing outagages. we have had various phone employees promise it will be fixed. we have had techs come out and leave because they did not have time to fix it. we have had others fix outside lines which didnt help, others never should up and now today the tech hung a missed u  tag on my door without even knocking. comcast has my contact number but insists on using my triple play land line number which was never even hooked up.  what should I do next.  i have a 1 year contract