Estate agents are evil

We moved out of our old flat at the beginning of December.  Right away, they sent us a letter saying there were some damages, outlining them, and stating that they would let us know as soon as they figured out how much they would cost.  We didn't agree with what they were saying, but thought that we would see if it was just going to be small amounts, in which case, we probably wouldn't fight it, as sometimes, it's easier just to let these things go.  I don't cope well with these kinds of confrontations.  3 months later, we finally get the next letter.  They have added multiple other things that we are supposedly responsible for.  The patio doors were apparently 'kicked in' and they are trying to charge us £271 for those- £1,300 in total!  They seem to have just made this up some time after we moved out.  They are full of shit and it makes me ill.  I have since read other reviews about them online in which people have had similar experiences with them.  I guess they make a habit out of taking advantage of people like us.  How lovely.