Returned faulty M-Board, company claims a different fault

I have returned a faulty computer motherboard and the Scan have said that the warranty is rejected.
The fault was: memory bank B would not detect any memory chips. All of the memory chips worked in the other slots.
The fault they list is not the same as the one that I had. They say the CPU slot is mashed, whatever that means.

I used to run a computer shop a few years, and I am still good friends with the people that I used to work with. I am also a qualified programmer in case extra proof is needed. I have built many computers, and I am extremely experienced.

From my perspective, regardless of this ‘new fault’ they claim the motherboard did not work due to a previous fault. Additionally I have not asked for it back but a replacement.
Maybe the tester messed up and damaged the CPU slot?

Curiously they offer insurance so that a customer is covered in case they damage components during the building process. I did not take this since I have not had a problem over my many years of building PCs.

Has anyone had a similar experience? How does the legalities stand, since they are basically disputing the problem and claiming that I have damaged the board.

Update:
The motherboard has a socket protector that covers the CPU socket, on the label it says this must be placed back over the socket if the board is returned. I can not find this cover, and I am sure I did it put it in.

Scan say that this was not done, and they claim that this is how the socket was damaged. They say they will be emailing me a picture. For all I know this picture could be off another motherboard.

Thanks for the links and I am now currently reading the articles.

Having read the various documents:

Scan offered to repair the item, and they say the new physical damage invalidates the warranty. However they will now not test the item, since there is a chance the damage to the CPU socket could damage any CPU used in the testing.
In the Staturary rights it says: "If a repair impossible or unfeasible, you must then be offered a replacement."

They say the new damage over-rides the previous damage and since they blame the damage on me, either removing the motherboard, or in transit.
So they say they have fulfilled the attempt to repair the item, and the fact the board has physical damage is down to me, and thus me damaging the item negates Staturary Rights.

Is this the case?