Finding title of old asian horror movie

I'm counting on your guys/girls expertise with this.  I haven't had any luck posting this inquiry in other forums.  Thanks so much in advance.

It's pretty old, but I hope someone can help with locate the title of this film. I believe it's a chinese film. I saw it maybe 10-15 years ago. Don't remember who stars in it at all, but my sisters have been asking me to find the title for years now cause they want to watch it again.

Plot goes something like this:
An old lady lives with her teenager-ish (?) aged son. The son's quite fat and doesn't really do much around the house. He's not really a nice guy from what I remember, kindy of creepy. Anyways, he's in love with his girl neighbor (?). The girl already has a boyfriend. Then I think the son killed himself.

The mother knows some black magic. She brought the son back (even though he was all gross and zombie looking). She kept him locked in his room/house. She then kept trying to kill the girl so that she could give the girl to her dead son as his wife. I remember there was a part where the girl had a birthday party (?) and just when they were about to eat the cake, it was all maggot infested (eww gross, I know).

At the end of the movie, I think they managed to kill the zombie son. The mom was trying to get back at her because she was crazy at losing her son again. The girl (and her boyfriend too? -- not sure) jumped off something like a building and died. I think that's how they escaped the crazy old lady.

Anyone got a clue? I'd greatly appreciate any help. Thanks!