purchased ipad pro 11, Apple charge more than invoice price

Sorry this is not a tech question... This is basic math question.

I purchased a new ipad pro during recent 2020 4 day sale event on Nov.27. The total amount for this device and gift card is $857.17 (tax include). I paid with $100 gc and $757.17 was charged to my account balance. After 2 weeks waiting, today Apple sent me an email said I need pay extra $57.17 to keep processing this order. I chatted + called Apple for 9 times to solve this issue, fianlly Apple noticed I paid in full already and ship the order today.

However I check my account balance, Apple finally changed $800 from my account balance and $100 from gc. It seems I got charged by $900 for this $857.17 order. $42.83 ending balance disappear.

Anyone know who can really solve this issue? I am already tired chatting and calling Apple.