H-E-B complaint: Embarrassed me in front of store

I spent 2 hours shopping and when I went to check out the terminal would not accept my ebt card. I checked the balance before I went in and I had over $300. So I called the SNAP help line and the lady checked the history on my card and said there was no reason for my transaction to be denied. The manager at HEB tried saying it wouldnt work because there was a scratch on the back of the card, but why would that matter if I put the numbers in manually. Which I did and the transaction was still denied. I stood at the front of that store with the manager acting as if I was totally stupid. My card was not the problem. I immediately went down to mini mart to get drinks for my grandchildren that were with me and the card worked perfectly fine. So I call the HEB to let them know that it was not my card that was malfunctioning and was completely dismissed by the manager. She told me to get another card. She refused to accept the fact that there was nothing wrong with my card. This morning I go online and use the same card and it worked. So what were the employees at the store doing to where my card would not work yesterday. It was embarrassing, a waste of 2 hours plus of my time cause I still have to reshop. I am disabled and was made to look like a fool in front of my grandkids and everyone else in the store.