Official Payments Corp. They did not post our tax payment to the IRS Internet, Internet

Short and Sweet:  People seem to be curious about Official Payments Corporation.   When you get a payment due notice from the IRS, or from any government agency, you want your payment recorded immediately.  We paid Offical Payment Corp. to process our IRS payment - and they did not post it to the IRS.  We don't know where it is frankly.  We just got a certified letter from the IRS demanding payment.  When we told the IRS representative that we have the confirmation number for payment, they told us it doesn't have any effect until the IRS gets the money.   The IRS told us that when we pay Official Payments, the money is posted immediately - it's been over a week, and the money still has not been posted.   We sent an email to Official Payments twice, and got no reply.  DO NOT USE OFFICIAL PAYMENTS IF YOU HAVE A PAST DUE, OR CURRENT PAYMENT WITH THE IRS.  They are not reliable and they are unresponsive.