Snail Mail Error

I've tried to invoice my customers with snail mail invoices. Some of them have been sent, but the majority of them have failed with an error. I tried to resend a few of them and get the same error. I called you guys back when the error happened and also sent a few emails. I have been told that it would be looked at and fixed. Well it hasn't been fixed and no one has contacted me about the issue since then. The invoices are due soon, and no one knows about them cause they never been mailed by you. How can we fix this issue.