US Treasury Check & CP21B don't match?

I recently received a check from the US Treasury, and an IRS letter followed about a week later (Notice CP21B). I was on unemployment in California last year due to the pandemic, and this year I filed my taxes as soon as I could, and I know California changed some of the tax aspect for unemployment (it was early February that I filed).  The refund amount listed on my notice is $20.84 less than the amount on the check I received. I don't want to deposit my check knowing there is a discrepancy between it and the IRS notice until I can verify the check is correct, or that I will get a different one with a correct amount. Who can I contact for help understanding what is going on, granted the IRS is hard to get a hold of?