That's an old lame trick. It happened to one of my girlfriends, her ex made her come over to him 2 times after she had officially moved out. Each time he'd make her coffee, and talk to her, and each time a few of her things got misplaced or couldn't be found when she got there, then later on they'd mysteriously resurface so shed have to come back for them or meet with him some other time. Third time I got angry and decided to go there myself. There was no need for a fourth trip, the dude was very efficient at handing me everything that was needed in the shortest amount of time.
Send someone else after your things. Try to get someone intimidating, so your ex won't want to deal with him(her?) again.