I'll assume both ends of the HDMI are fully seated because Contour indents something.
This is what I think: RCA used to be 1 company but has been historically bought and sold by other companies. I don’t know which company owns RCA now but I’ll assume whichever company, the company probably owns 10 other brands of TV sets but buys…or owns…1 type of IR component and this 1 component has to be compatible with a hodgepodge of mixed-and-matched components of the 10 other brands. This is probably why the Xfinity site lists 50 IR codes for RCA. You’ll just have to trudge through all codes.
If you finally find a code, make sure it not only works for Volume and Channel but also Mute and Input Select from the Contour remote. Input Select instructs the TV to display whatever is connected to it.