We are selling software using 2checkout payment gateway (our client can able to download when 2checkout.com Orders reviewed – Passed)

My current problem:
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We realize after purchase our product (when order is passed from 2checkout.com) some clients ask for refund after 20 days / 30 days even 60 or 90 days via 2checkout.com

When client ask for refund via 2checkout.com MOST OF THE TIME 2CHECKOUTC.COM ASK US FOR FOLLOWING INFORMATION:
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Please provide documentation to prove the cardholder participated in the transaction. Documentation should include a signed sales draft, signed imprint of the card, website print out, Verisign transaction detail report, or bill to and ship to address.

And all the time we failed to provide above information because client buy our product from our website and we provide link for download our software when 2checkout.com passed clients order.

Now what we want:
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We want to inactive refund after purchase our software once its passed from 2checkout fraud department.

Please let me know how we can stop refund from our vendor account. If needed we can accept or add any terms and condition or please let me know if there is any other way to stop refund from our vendor account.

Thanks in advance.