Landlord charging for wind damage?

Hi, I was renting a flat until march this year (AST), late last year I returned to the flat after a weekend away to see that our back yard wall had blown over (a neighbor seen it happen). The next day our landlords agency had sent some guys round to clear the mess, I heard nothing more from them after this and also the landlord changed agency shortly after, the wall stayed down until we moved out this march. We have recently received a bill for the wall and I think this is unfair as it was notdamage caused by ourselves.

Here is a photo from google street view of the wall before the incident.
and then the the wall just before the guys came to clear the mess.




Please advise me on how I can handle this situation, I don't want to contact them until I get some advice.

Thank you.