[Client] - Overcharged on Riot Points

So today I went out and purchased a pre-paid $50 Riot Points card from Walmart and redeemed it giving me a total of 7702RP on my account. After purchasing Viktor(880RP) and the Creator Viktor Skin(1350RP) as well as Nautilus(975RP) I had a remaining balance of 4497 RP I then proceeded to purchase the Redeemed Riven Skin for 975RP which should have left me with 3522RP but instead I was charged an extra 975RP leaving me with only 2547RP. My hopes were to purchase a couple of the new skins when they are released but with the overcharge I won't be able to. If someone from Riot could please get back to me with either and explanation if there is a valid reason why I'm missing that extra 975RP or a correction that would be great I have spent a lot of money on this game through Pre-Paid cards and would really appreciate having all that I payed for.