I told them both times that the only reason I signed up for Walmart + was because it came as a benefit with the Amex plat card. I explained on today's call that the credit was only received if the membership was charged once per month and that it's unfair to me that due to no fault of my own I would now need to lose out on getting 6 of those credits. The rep apologized and said they were aware of the error and were working on refunding the extra charges.

I'll wait 2 weeks and if I don't get any credit I'll know that what your rep said was correct and will dispute with Amex as per Walmart's own suggestion.