Customer needs to lodge his complaint with the IRS and work through their process to get the funds directed to him correctly.
What Happy said; the IRS expects the taxpayer to complain to them and let them deal with it. From
IRS Guidance: What actions should be taken if an RDFI is contacted about a claim of non-receipt of a tax refund?
An RDFI may be contacted by Treasury Fiscal Service through receipt of a 150.1 or 150.2 Form, notifying the RDFI that one of its accountholders is claiming they did not receive their refund. If an RDFI receives a 150.2 Form, it is only responsible for contacting the accountholder and taking any necessary measures listed on the 150.2 Form. However if a 150.1 Form is received, an RDFI must respond to Treasury Fiscal Service within 3 business days of receipt. If the payment was misdirected to the wrong account and the funds are still available, the RDFI may be asked by Treasury Fiscal Service to return these funds to the IRS using the R06 (Request per ODFI’s Request) Return Reason Code. Green Book discussion and examples of Forms 150.1 and 150.2 Just a suggestion, if I found the consumer's payment and realized it went into the wrong account because he gave the IRS the wrong number, I would not tell him that. I would tell him to go through channels and let the IRS tell him that he gave them the wrong account number...
"Ees not my yob" to deal with this and, if I try, it will become readily apparent that I cannot fix it, but will stil be stuck listening to someone whine about it.