I've saved many of mine that were impacted & the vet had oiled & still couldn't get them unimpacted...as I give mine a warm water mixed with half bottle mineral oil enema.( You can use plain warm water also). I just use a regular red enema bag(human) & put about a gallon in them(lube the end with Mineral Oil & put it in about 6 inches, then wait a few minutes. Be sure to use the little short smooth end that's for giving human enema, not the other attachment that's for giving douches. If they're really clogged & won't hold much water, you just have to keep putting it in a little at a time till it gets unclogged...sometimes it takes several gallons to get them unclogged, but you will know when they are, as they will start wanting to eat & not lay down.
Be sure to stand to the side of their rump out of the way of them pooping as it will squirt water straight out when they expel it.
I will then mix a half pint to a full pint of mineral oil in with a small amount of feed & wet or water soak their hay for a few days also.