Affiliate Marketing Secrets

I work in e-commerce and we have recently discovered that our affiliates are automatically getting paid, even if the payment for the product failed.
Our website hosters who deal with our affiliate marketing are now claiming that we have to manually cancel any commissions on payments that fail (we have never been told this!), but seeing as we never received payment in the first place, surely this isn’t right?
We are now over £10.000 down for sales that never completed and were probably fraudulent! Has anyone had any experience with this as an affiliate merchant? Is there any legal leg for us to stand on as neither our hosters/marketers, nor affiliate company are taking responsibility. Any advice would be greatly appreciated. Thank you in advance.