I saw this film on TV approx 1980

It is about a couple who loose a child and dabble in black magic to bring him back.

I thought it was called Billy and had something to do with Franco Zafferelli.

The kid doesn't com back, he sends satan instead.

the film is only about 45mins long.

Can anyone please tell me what it is called? Where i can get a copy etc???

Many thanks,

Billi nelson