By far the easiest is to take the TV boxes and power supply's back to your local Comcast office, (if within range). Be sure to obtain a receipt for items returned and keep it for years.
However, if in a contract, you could be subject to an ETF. Also if on promo pricing, dropping a service could mean that you may end up paying more than you were before. There would be less discount (if any) for a double play too!.
Hi Corena1911, If you still need assistance I could help here as well. Please send me a private message with your account information (your name, address and account number).