回複：租房合同還有半年到期，想提前搬走，被告知要支付全額租金除非

I am in Maryland, but don't know if there is a specific law provision on rental matters. That provision should be in the contract you signed when you rent the apartment. Check on the paper. It sounds like a conventional practice in renting. If there is no provision as such in the contract, then you have a chance to argue.