Hello Chloe, welcome to Just Answer.
A bit about Proscan. It was at one point made by Thompson as the high end model following the dimentia line, now they replaced it by the scenium line. In 2006 Thompson licenced the logo and the name (those are still owner by Thompson) to ON Corporation, that now manufacture them (so they are no longer RCA TV).
The code needed by the universal remote is dependent on the universal remote maker (as you can see in the proscan manual those code are different depending on the brand).
You can always try those code first but it's not sure they will work (the philips
ones given have the biggest chance to work as philips do cable box.
If none work you may look into your cable box booklet for a "code search" or an "auto search" procedure. That will try a new code each time you pres a button. This will eventually cover all the remote internal database set of signals.
If this fail, then it's not possible to control that TV with that remote. in such a case, it's possible to get a remote with learning capability. Here is one for example:
That remote can record any other infrared remote, so you are not limited by a set of code. You can enter both the comcast and the proscan remote in that one.