There seems to be a couple of design faults in the hedgehog house which allow small cats to enter. Ideally the entrance should be on one side of the front rather than the middle. This would make the chicane harder to navigate for longer animals. Also the height of the entrance, at 6 inches, seems rather large. Hedgehogs are good a squeezing through tight gaps.
As a quick fix I screwed a piece of wood inside which reduced the height of the entrance from 6 inches to about 4 inches to see whether that will deter the thieving moggy.Also the food dish is now right at the back of the house.
Only time will tell whether that will do the job.