Have you tried using TEdit to remove it?
Terraria Community Forums
UltiDaniel
The Storm
Try creating a 3 block wide tunnel around the corruption and filling it with wood or a non corruptible block.
ChipperCrow
to clarify, i have a 'normal' terraria world. there are bits of the corruption that i can't get to, mostly underground, that are beyond the reach of the clentaminator. also, what is TEdit?
UltiDaniel
A program that you can use to create, remove, or change things within your Terrarian world.
BrusselSprouts693
It can't corrupt it if it's already hallowed