OP - This may be hard to accept, but the best thing you can do is to wait. Calling will not change anything and there is nobody who is going to go looking for the bag. When you call in, someone is simply looking at a display and telling you some version of the same thing.

If you are being told the truth and the bag did make it to ATL, it will either turn up or it will not. If its baggage tag is still attached all the better. Hopefully you have put a personal tag on the bag and inside so that you can be matched if the baggage tag has fallen off. If it does not turn up, it has possibly been stolen or was severely damaged and someone tossed it to get rid of it.

At 20 days, e.g. on the 21st day, you may claim, as noted above, the fair market value of the bag and its contents. The Montreal Convention provides a maximum of US$1,660 (approximately) and you may be asked to present receipts for out-of-the-ordinary items. Also note that fair market value does not necessarily equate to replacement cost. A $200 shirt worn 5 times is not worth $200.\

Finally, it is water under the bridge for you, but for the sake of others, make sure that you have insurance. If not through a credit card as in this case, then purchase a policy.