This is my advice…
Don’t move until the 30th June. I assume you have some contract with uniplaces.com or some documentation that you are renting until 30th June.
The law is very heavily on the side of a tenant in Spain. But above that there is a moral issue here. The landlord has rented you a place and now his plans have changed he doesn’t care about the tenant, I find people like that morally repulsive!! You have the keys so just continue to live there. Call the police if you are subjected to hassle or you find you come home and the locks have been changed.
Also speak with one of the citizens advice agencies in Spain on what are your legal rights. But I think you will find they can’t just throw you out or change the locks, or even cut off water or electricity.
Good luck