Sorry to hear you are still having trouble, A500 mats are really confusing.
I managed to take some photos of my mat fixings the other day and I've added an image of the exact mats I have, these are a perfect fit (including the passengers one) in my 2013 595c Comp, manual, right hand drive. The blue square shows the area of the driver side mat show in the other 2 photos.
The other photos both show the different fixings. The mat is not in the correct position, it's been moved slightly to show how they attach.
A is the hole predrilled in the car (the larger white hole). The hole is through the carpet and in the metal floor underneath. I'm not sure what the 4 other smaller holes are they seem to be lugs help make sure the carpet is located in the correct place.
B is the aluminium screw that fixes into A. For some reason I only have 2 of these.
C is the plastic lug that came with the mats. These have a shallow thread underneath that screws into the pile of the carpet. They don't attach to the metal floor in any way. These can be located anywhere on the carpet, this one is in the correct place for the drivers mat to fit in the correct position.
D is a fixing prefitted into the mat, It clips onto C and keeps the mat secure.
I bought these mats expecting to use B to fit through D and then screw into A but as you can see they don't line up. In the end I had to fit the C's into the D's, lay the mats in the correct place then, while still clipped into the D's, screw the C's into the carpet.