@Ray10
Sorry that you have made such a bad experience with this community.
It is really both your good right and your duty to inform the host about any problem that you encounter on his premises. If the prompt reply and action are NOT forthcoming, report the matter at hand to Airbnb with photos and all the available documentation, and start claiming the refund right away. Ask the Airbnb to help you relocate to a better listing in the neighborhood, too. The sooner the Airbnb knows about the issue the better.
Claiming the refund once you return home may be far less efficient. You claim that the flat was filthy, etc., and the host would say that it was spotless. You are facing a typical situation of two people making two opposite statements on the very same matter. Since you are claiming at least a partial refund, it is really up to you to prove that your claims are well-founded. Once you get home, and the impression is created that you spent all the booked time in an unsatisfactory listing only to claim the refund afterwards, everything becomes a bit more difficult with your claim.
Think of an analogous situation in a restaurant. If the food you received is really not what you ordered or is not good, return it immediately after the first bite. You will not have to pay for it, and can look for a different place. If you somehow ate the food the chances are they may not be very forthcoming with the refund.
If you find this information helpful, consider clicking the Thumbs-Up icon near lower right. Thanks!