Hey there!
The entire game was written quite long ago from scratch using our own engine, developed in C++. It is a bit dated and therefore controller support was never officially supported or heavily tested.
We are working on a new version of the game (very, very slowly) with controller support added. We still don't have too much possibility of testing (other than with our own controllers) so once the game's new version is almost ready to go, we will get in touch so that perhaps you could give it a try for us :)?
Thanks and apologies for the inconvenience!