<human>: So here's the deal:

Last month I purchased a shiny new power supply ($90) from newegg.com.  I used my "Preferred Account" which is their financing option and is run by "Bill Me Later".  After the order goes through I immediately remember I forgot to add my gift card to the purchase, so I call them up and they cancel the order for me so I can repurchase.  They mention the refund will go through in about a week, and I go and repurchase the item with the giftcard for a total of around $40.

To my understanding, this should have left the account with a $50 credit, expressed as a balance of -$50.  However days go by and my account remains at -$90.  About a week later I buy a desktop case for about $50, which goes though and brings my balance to -$40.  Both the case and the power supply are in my possession and are recorded in my order history as successful purchases.

I just received my statement for the month of April, with the balance of -$40 still displayed.  I called up the Preferred Account Hotline, and the CS rep notices everything as I had mentioned and explains that since the account is managed by a third party, it is possible the mistake is on their end.  She also told me that to her knowledge there is no incoming charge to the account that is invisible to me, nor is there a flag of any sort indicating an error.

So my question: is it ok to assume that the credit will remain as is until I spend it.  I noticed a deal on an item I was interested in, but would not otherwise have the money for without the $40 credit that is in my account.  Is there any sort of definite rule or law that states once a statement is released, it can't be altered?

Thanks for your Help

Can you condense the text into three sentences or less?
<bot>: Bought an item, did not get charged, Monthly Statement did not show the purchase, Can I take advantage of their mistake?