@lauralud36 - so here is the conflict
1) you can't find record of receiving the $4200
2) but the IRS records say they sent it to you (which is why they adjusted your tax return)
so you would have to submit a 'tracer' to the Treasury Department (See link below) to determine if the check was deposited, what bank account, or is not cashed, etc. The IRS has nothing to do with this, so no sense contacting the IRS at this point.
https://www.irs.gov/pub/irs-pdf/f3911.pdf