Below is exactly what the IRS instructs taxpayer to do with checks received incorrectly.   There is nothing wrong or incorrect with what they did.   The IRS is a MESS - I guess this is just one more thing they'll have to figure out(i.e. screw up) this tax season.   As long as they keep letting unproductive and unsupervised employees "work" at home - these delays/errors/etc. will continue.

IRS States below:

A1. You should return the payment as soon as possible by following the instructions below.

If the payment was a paper check and you have not cashed it:

• Write "Void" in the endorsement section on the back of the check. Mail the voided Treasury check to the appropriate IRS location listed below. Don't staple, bend or paper clip the check.
• Include with the voided check a separate, brief, written explanation stating the reason for returning the check, including whether you want to unenroll from future monthly advance Child Tax Credit payments.