Tenants refusing to pay for some damage, is it worth trying to get the money?

The tenants broke glass in the back door, they said this was because the door was stiff, but was no problem previously.

The tenants broke a key in the front door lock, they are refusing to pay for the lock as they say the key may have been faulty. The key was in use for some months before they moved in and about 5 months after they moved in with no problem.

There is a burn on a carpet that was new when they moved in, the pile is melted, they are saying this is fair wear and tear.

They wrote a phone number on the top of the new fridge - the pen has not only stained but indented the paint. I want to charge £50 for this but they only want to pay £10. This is not covered under the guarantee and will eventually cause rust.

Please could you advise on whether it is worth taking these issues to the DPS or whether to just accept the loss.

Thanks.