Charged less for a large purchase

[MLE]

I have a purchase from a company which I know is doing a lot of fax-in and phone orders (mine was faxed). The original purchase price was 1144.80, but I was only charged 114.48. This means they have my credit card and expiration date on file and have the ability to charge me a second time without further contact.

How long do they legally have to correct this mistake before they're legally not allowed to correct it without contacting me?