As you were directed, for Walmart discounts you need to handle it thru Mywalmart.com or the intranet at work where you take your CBL's, VZW stores can not handle Walmart discounts. But the employees are not aware of this.
If you used your personal email address, you should have received an email back confirming your acceptance.
Once accepted, the next invoice will show the discount.
You have to sign up through myWalmartBenefits to get the 20% discount.