I'm really sorry that happened to you. I don't shop at Wal-Mart simply because I have, shall we say, a moral opposition. I have plenty of other options where I am now, though. However I do remember when I lived in NH in the early 90's, WalMart was pretty much the only game in town unless you wanted to drive to Keene. And even there your choices were pretty limited after they shut down Bradlees.
Anyway, I had a situation one time where I was taking a snapshot of a piece in an art gallery. I didn't realize that photos were limited to only the permanent collection,and apparently the security guard was trying to tell me several times that I wasn't allowed to take photos. I'm HOH, and in the cavernous gallery space with the ambient noise, her little whispered "excuse me ma'am"s were completely lost on me. Never heard her. Finally she was in my face, telling me, "YOU CAN'T TAKE PICTURES IN HERE!" and I apologized, but she rolled her eyes, looked at another guard, and made this gesture that was like "God! What a MORON!"
So I simply explained to her that I was hard of hearing, and she said, "Oh. Well, I don't know that." And I said, "No, you wouldn't. Not by looking at me. But by the second time that I wasn't responding to you, you should have come up to me then instead of making a scene and causing embarrassment to me." She copped a huge attitude and never even apologized. I sent a letter to the gallery but I never got a reply. Figures.
Another time I was in a situation with law enforcement (a really, really long story that I don't feel like telling), and I explained to officers that I was hard of hearing. Then at one point one of them was going through my wallet and she made a comment about "all" my credit cards (like whatever, I had three. And one was my bank card. Ooohhh....) and I said, "what about them?" and she looked at me and said, "I thought you said you was deaf!"
God damn it, it's just so frustrating sometimes, it makes me want to stay home and never go out.
I can't wait to find out how Wal-Mart responds. But, keep in mind that they're not particularly well-known for their sensitivity, so I won't be surprised if you get nothing in the way of a sincere apology.