New digital TV reception

I am so unhappy with the reception since I got the mini boxes for the new digital cable that I am seriously thinking of calling to cancel. I would rather just watch Netflix or Hulu then constantly have trouble with a service for which I am paying so much for.

 I am unable to get NBC, channel 3, nor can I get 4,5,6,7,8,9 and most of the time the guide does not work either.  I have called and spent a lot of the time on the phone and then it will work for a bit then I lose it all again. I have tried unplugging the mini box and letting it sit awhile but I never get all these lower channels.

This last week I have been having trouble with other channels looking scrambled, it just comes and goes.

The last time a tech was here to pick up my recording box because I thought it was the problem, he said he thought it was my wiring. He said my old cable wire isn't current enough and he could replace it for a cost.  Well I don't have wiring per se. I have ONE wire that connects at the wall where the one Cox cable comes in.  Can I just buy a new length of wire and change it out myself? I am on social security and I certainly cannot afford to pay a tech to do something I am perfectly capable of doing myself.