The last couple of times they have failed to email it to me. You can get it by either calling Disney Research and Billing Team at 407-828-5630
or you can email
guest.services.billing@disneyworld.com.
Include as much info as you have: for example, your name, resort, room #, your travel plan #, your dates, etc. Also provide your email so they can send it.
When I emailed, I got an answer the next business day.
Also, they usually wait for 3-4 days after your stay before sending it to allow any straggling charges to come in from the parks or Disney Springs. If it has been 7 days or more, I would use the channels in the first paragraph.