Hi all,
My partner and I recently adopted a cat (4 years old, all up to date on vet treatments, generally good as gold). She's settled in really well, which is great. She's been really well-behaved, knows her meal times like clockwork and has no problem using her litter tray.
However, she has clearly been confused by our doormat - it's integrated, i.e. part of the carpet, right by the front door, and must feel notably strange on her paws. Anyway, she's clearly concluded that it's a second litter tray!! The past few days she's weed on it several times, and once even pooed! 
But she is also still using her normal litter tray.
We've been trying to block off the area/close off the hall at night, but it's pretty impractical to basically barricade ourselves in by closing off the front door. We've tried Urine Off and another similar brand, but no success. Has anyone had anything like this before, and any tips in how to make her understand not to go to the toilet there?? I've read a lot online but it's generally about cats having anxiety/unhappy with their actual litter tray/being unwell, whereas here, our cat genuinely thinks the mat is a litter tray!