You can find the receipt of your on-line purchase in the e-mail that you received from Kaspersky. If you can't find it, you can try to retrieve your Activation Code. This is found on the CD sleeve or card, or in an email, depending on if the purchase was boxed CD, or on-line. If you cannot log into your Kaspersky account, or you cannot locate your activation code, you should contact technical support at the following web-page.
You can also check this forum to find out more about this problem.