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It is possible that the IRS never did receive the payment. Generally when you go through a CPA or Tax attorney you still make out the check to the IRS directly not the CPA or the Attorney.
If you made a check to the CPA/Attorney then you first need to speak with that individual and get a statement that shows what you paid and stipulates what the amount was for.
If you made a check out to the IRS get confirmation from your bank that the funds were accessed (the check was cashed).
Please advise if you need more information or what you found out from the CPA/attorney.