Hello, i would recommend to use Python, you can use matplotlib library to make heat maps. it's quite flexible but you must be able to program with it and understand the structure of the code. If you already know some programming language, it will be easier.

You may search on google: "discrete heatmap python", and also check some part of this:

https://community.plotly.com/t/colors-for-discrete-ranges-in-heatmaps/7780

https://stackoverflow.com/questions/40853556/3d-discrete-heatmap-in-matplotlib

You can use R. But any practice and knowledge in python will be so useful for you future analysis.

I think this kind of graph could be recreated using Python with the seaborn or matplotlib library.