Yeah, I did all those things they suggest several times. It hardly ever seems to work for anyone, but they like to get you to do something as it means they can tick a box saying they have advised the customer how to fix the problem. It’s always something that will take a long time too, so you feel obliged to thank them and say that you’ll go off now and try it. I always like to freak them out and say, “Hey, stay there and I’ll do it right now.” They don’t expect that and usually respond with something like, “Oh, it might take some time and I’ll need to help other customers, but if it doesn’t work then feel free to get back to us.” To which I usually respond, “Here’s an idea then. Tell me all the other possible solutions and I’ll make a note of them to save you and your team time if your first, second, third, … solution doesn’t work.” It turns out they don’t have any other solutions.
I’m ranting again. Can’t you tell I’ve been there so often before?!
To be honest, I suspect it’s an Xbox Live servers issue. At one point, when it happened to me, I was able to discover that there was a major Xbox server outage on the day my achievement didn’t unlock and thousands of people were affected. If that’s the issue then nothing you do at your end will first it. You just need to be patient.
I know you’ve already done it a few times. However, on the off-chance it is to do with the challenge not properly unlocking then I’ve just created a brand new account on the Xbox, completed the challenge, and the achievement unlocked. I also re-did the challenge a couple of times and the associated Easter Egg worked every time, so if you’re not seeing the tears of blood and hearing the elephants roaring then you definitely haven’t shot all 18 elephants. Here’s a video I made to show you how I did it. You could probably start as a security guard if you’ve unlocked the start location, but, as I said, this is a brand new account, so I had to start at the default location.
There is extra information found in the notes below the video which may help.