https://account.battle.net/transactions?tab=2
Go there then click the “virtual wallets” tab. It will bring up Traders Tender. Clicking on Traders Tender amount will bring up a breakdown of expenditures and earnings. See if you’ve earned more than 500 in April. If so, you already received the “free” tender.
If you think it’s still not acting appropriately you can also move this/post over in the Customer Support forum. A Support Forum Agent may be able to look at your history and see what was credited.