Did not receive adjusted refund amount in CP49 Notice

Hi All,

 

I had a payment plan in place from 2016 and part of my 2020 refund was used to completely pay this off. I received a CP49 notice stating this. The notice stated what my adjusted refund would be. My issue is I did not receive this amount when I received my refund. I received ~1800 less. I cannot get through to the IRS as they are busy and the line hangs up. Any suggestions?