Leaking door threshold

doctor40

Would be grateful for any advice. Had a new door fitted about 2  years ago. The fitter was back early on to seal what seemed to be a couple of leaks. All settled fine until about 6 months later when there was a smell. Lifted the carpet and the floor was wet. Hadn't had various damp proof people etc and no one could work it out. Anyway on closer inspection it seems the door is leaking. The concrete floor is getting wet between the bottom of the threshold and the floor. The skirting at either corner of the door is also getting a bit rotten. 

The fitter came back last week and sealed inside and outside the threshold. There's been a lot of rain and where the floor was wet to touch at the threshold/floor junction there's now pooling of water. The gap between the threshold and the door is dry so it seems like it's somehow under the threshold. Not sure where to go next?