Host asking for more than 400$ reimbursement for wear and tear and Airbnb allowed it [Serbia]

I stayed for 6 nights at this place in Belgrade, Serbia.

From the pictures it didn't actually show the apartment was below ground, so when I went in, I was surprised by the damp and mould smell I witnessed. It's fine, my bad- didn't zoom in in the pictures while browsing (not the case, lightning tricks done by the host so you won't notice).

Okay, I come in, there's a sofa bed, not an actual bed. Okay again, I'm beat from the road, I need to sleep off a bit. Went ahead and did the bed as one should, and noticed a big ass dent in the middle. Fine, I'll sleep on the other side, as I did.

During sleeping, I would roll on the other side, notice how uncomfortable it is and I would roll back on the "good" side. Thought about messaging the host, but hey, this is actually wear and tear, people slept here before me and it is expected for the "bed" to be uneven.

Left the place and then the host messaged me that I broke it!!! What the actual f! I weigh barely 50kg, even I wanted to, I wouldn't have been able to break it, unless I jumped on it (which I did not).

Submitted evidence to Airbnb of the bed, you can clearly see the dent and depression. Still, Airbnb ruled that I BROKE the bed frame.

How can I solve this? I'm on my Witt's end and on my second appeal. This is not fair, I refuse to pay for damage that was caused preciously!! Plus, the price is way too much.

Any advice is welcome. Thank you.