I didn't move in, didn't take the acceptance key, didn't sign a contract with the property management, and the purchase contract signed with the developer had no property terms.

You have been the owner since you signed the purchase contract with the developer. Although you didn't move in, your rights and obligations have come into being. Therefore, according to the relevant provisions of the Property Law, it is reasonable and legal for the property to charge you 30% or 20% of the property management fee, which supports the property from a legal point of view. But you can negotiate with the property to see if you can lower the discount on the property fee a little. After all, the relationship between the property and the owner is to serve and be served. Don't be too stiff, which is not good for anyone.