@Pier-Olivier0
If you cancelled immediately after the booking (within 1 hr of paying for and confirming the booking) then it is the Airbnb system that did something wrong with your cancellation and refund - NOT the host. There isn't anything the host can do to help you..... except contact Airbnb and take the guest's side in saying that "Airbnb looks like you made a mistake, please rectify".
The host doesn't have your $700, Airbnb does. The reason the host blocked you is because you kept asking for money the host never got or saw. The host did nothing wrong, simply tried to help by sending you a link with the hope that it would help you get your money back from Airbnb, but you ended up demanding the host give you the $700. Maybe the host could have explained how things work better to you..... but if someone kept insisting I had to "give money back" when I never saw a dime of their money, I'd probably block them too.
I agree you were treated unfairly..... but it was not by the host. There is nothing the host can really do and the host has no obligation to help you address a problem that clearly happened because Airbnb system sent you an email in error. If you want to get your $700 back, please continue to contact Airbnb CS.