Amended Refund Amount Different from Requested

I amended my 2019 return.  After over a year I received an amount which was around $600 less than what I requested.  I got a CP21B notice which said "We made the changes you requested" but there is no explanation for the difference.  It says that if I do not agree that I should call, but I cannot get through.

 

Should I deposit the check?  How should I get an explanation for this?  Should I try writing to them by conventional mail?

 

Thanks,

Moses