I am being charge for a slight stain on my mattress (I hadn’t even noticed it was there, landlords have sent a photo and it is only slight). The tenancy agreement stated that I must use a mattress protector (which I did, and it had no stains on it, so I don’t know a stain got through to the mattress). They are wanting to charge £100, the full cost of replacing the mattress. I feel that this is unreasonable as the stain was very slight, the mattress is still useable, and I made reasonable efforts to prevent any damage. On top of this, I agreed to pay a fixed fee to cover all cleaning before I moved out that meant that I was not responsible for any cleaning before moving out. What can I do about this? I know that the deposit is protected but I don’t know who with.