What should the developer do if the new house is not closed and does not bear the property fee during the maintenance period?

Let's go through legal procedures. It's simple. A lawsuit is accurate. First of all, the house was not sealed because of quality problems, and the developer maintained it for half a year. This is considered as overdue delivery, and the opening of the house will compensate you for the liquidated damages. This amount of money is quite large and must be compensated. The property fee is subject to the actual delivery date of the developer, so the property fee for this half year is not within your performance scope and can be exempted.

I suggest you sue directly, so you don't have to argue with Fang Kai.