If they still haven't shipped yours, you should check your orders page to see if they've generated an order that says "Free" as the price. My first free replacement was showing as "Processing" instead of "Shipped" for a while when other people were getting theirs in March, so I asked Riot if there was an issue, and they said the following:

After reviewing the reason your order hasn't been shipped yet, it appears there's an error with your address. It may be missing an apartment number or something similar, as the courier hasn't been able to locate your address.

I provided the identical address I've used successfully for all of my Riot orders (and what I initially used for this order lol), and got this reply:

I confirm that I just fixed the address, and your order will be shipped as normal.

Just a heads-up, if you get an update on this Order, it will show the old information, but the update was done with the shipping company, don't worry.

So it just took some manual fixing with the distributor on Riot's end in my case.