What is the best way to replace defective equipment

I am currently having several issues with my Comcast Equipment (listed below).  What is the best way to get replacement equipment?  Is there a way to request it online or do I need to go into a store?

My issues are as follows:

1) My main box fan is very loud and runs all the time.  We also frequently get pixelation on the TV screen.  The box is a XG1-P Model Number PX013ANM.  This box is connected to a 4k TV.  How can I get an XG1v4 as a replacement?

2) I have a dead XiD-P, it will not work at all, needs replacing.

3) Over the past year, I have upgraded all TVs to 4k TVs and I can no longer pair any of the remotes to these newer TVs (I've tried the on-screen programming and dozens of codes I've found online - nothing will work).  Also, none of my current boxes support 4k.  How do I get boxes and remotes that will work with my newer TVs?  

Please advise!  Thank you!!