Reminds me of...
The Wicker Man (1973)
Crowhaven Farm (1970)
Race With The Devil (1975)
You're totally right about the Wicker Man.
They seemed to pretty much take the story directly and supplant a female love interest instead of the missing girl.
But at least in the Wicker Man it was a group attempting to return the health of the harvest to their crops. In this it's apparently the power to prank call messaging machines.