@Cibele18 Here is a screenshot of airbnb's cancellation policies that host can select. From what you have shared it appears your host selected the "Strict." When you make a booking and confirm, you are entering a contract in which you agree to the policies encompassed within the listing, including that nice cancellation policy.
Unfortunately, while you may deem that policy unfair, you agreed to it, whether you actually took the time to read the entire listing or not. When I was brand new too booking, long before becoming a host, I had the same thing happen to me. To say I was mad was an understatement, but in the end the host was in the right, and I should have read the listing better. The fact that your plans got cancelled has absolutely nothing to do with your refund. The only time a change in plans warrants a full refund is if you qualify for the extenuating circumstances policy, which is something like a death (Proven) or disaster.
I would suggest asking the host to consider refunding more on the grounds that he/she is able to rebook those dates. Since you are so far out from your actual check in, there is a higher probability the dates could be rebooked.