[xeroinfinity]

Did you use brake grease on the slide pins and other places and things that would slide ??
So you just replaced that 1 ?

They are supposed to be replaced in pairs to work properly.

Also the calipers might need new pad retainers/antirattle springs/slide pins(sold in a kit) that help push the pads off the rotor.

That would be why they are not returning.
Or that piston in the caliper is binding.

hope that helps